There is an almost infinite number of writers who speak on why they are writers (it seems the standard entry fee to being a writer is talking about being a writer). Many say: 'It's my nature.' Being a writer owes much to the future perfect tense; less about 'having had written' than 'I will have had written.' A writer is someone who must write because he is a writer.   I appreciate the circular logic to this and how frustrating it can be to writers who think they must pen a National Book Award Winner before they become a writer. And no wonder, whenever I say 'I am a writer' people rejoin with 'But what have you written?' Is there any way to become a writer except to be a writer?     
An opposing school of thought can be found in the writings of Dorothea Brande, Anne Lamott and Dani Shapiro - all creatives/teachers who argue that discipline and activity can make one a writer.     
My advice is never mind what anyone else says anyway. You do not exist in the minds, mouths nor ears of others neither does your writer-ness.

George Orwell's (June 25, 1903 – January 21, 1950) self-examination as a writer, Why I Write, expresses a slightly different motivation. Orwell saw writing as a response to external stimuli - in his case, a feeling of injustice - rather than an internal compulsion to express (although there is a fine line between the two).

"Shift" 2018—a layered porcelain creation by Irish ceramicist Anne Butler. Photograph by Vizz Creative.

Unlike Vincent van Gogh and Charles Darwin, who sought careers in the church before they settled in their respective careers, Orwell felt a literary summons at an early age.

From a very early age, perhaps five or six, I knew that when I grew up, I should be a writer. Between the ages of about seventeen and twenty-four, I tried to abandon this idea, but I did so with the consciousness that I was outraging my true nature and that sooner or later I should have to settle down and write books.

[...]

I had the lonely child's habit of making up stories and holding conversations with imaginary persons, and I think from the very start my literary ambitions were mixed up with the feeling of being isolated and undervalued. I knew that I had a facility with words and the power of facing unpleasant facts, and I felt that this created a sort of private world in which I could get my own back for my failure in everyday life.

Close-up of "Shift," 2018 by Anne Butler. Photograph by Vizz Creative.

George Orwell was a writer from desire, talent, temperament, and need as a child and an adult. He assigns four motives to writing. The first is desire, which he calls "Sheer egoism." He continues, "Desire to seem clever, to be talked about, to be remembered after death, to get your own back on grown-ups who snubbed you in childhood." There is a subconscious egoism happening as well, the desire to play god with characters.

Second is what I call 'talent' but Orwell names "aesthetic enthusiasm," which is a love for the beauty of the art. "When I was about sixteen, I suddenly discovered the joy of mere words, i.e., the sounds and associations of words." Creating something new, original, and beautiful is certainly a motivation, although it rarely persists alone.   I typically find it impossible to write for writing's sake, or to paint for painting's sake. Yet I read Neruda's Odes to Common Things, Jason Reynolds' zest for the creative spirit, or Brodsky's love letter to Venice and remember Emerson writing there is miracle in the commonplace and I think perhaps we can divorce aesthetics from politics/culture/society.  
Orwell, of course, disagrees:     
 "The opinion that art should have nothing to do with politics is itself a political attitude."

"Shift," 2018 by Anne Butler. Photograph by Vizz Creative.

Orwell calls "Historical Impulse" the third motive for being a writer, "Desire to see things as they are, to find out facts and store them up for the use of posterity." This is contiguous with his fourth reason: political purpose. I suggest 'temperament' as a more suitable third (a desire to make a company out of loneliness, etc.), but this is Orwell's ego operating here, not mine.

Finally to number four, the most critical to Orwell - a deep motivation to unseat accepted social injustice.

Political Purpose - using the word 'political' in the widest possible sense. Desire to push the world in a certain direction, to alter other people's idea of the kind of society that they should strive after. Once again, no book is genuinely free from political bias. The opinion that art should have nothing to do with politics is itself a political attitude.

Number four was the one motivation Orwell lacked as a child (and thus why he wandered from writing many times in his life) and yet his primary writing motivation as an adult.

Orwell's poem was written when he was eleven and published under his real name, Eric Blair. The poem was published on Oct 2, 1914, as a rallying cry for patriotism. © Henley and South Oxfordshire Standard.

How did the child 'unserious' writer become the adult political writer? The answer is slowly, cautiously, with much self-awareness but inevitably because of contemporary circumstances. To paraphrase Orwell, 'one cannot not write about things such as Hitler.'

What I have most wanted to do throughout the past ten years is to make political writing into an art. My starting point is always a feeling of partisanship, a sense of injustice. When I sit down to write a book, I do not say to myself, 'I am going to produce a work of art.' I write it because there is some lie that I want to expose, some fact to which I want to draw attention, and my initial concern is to get a hearing. But I could not do the work of writing a book, or even a long magazine article if it were not also an aesthetic experience.   Orwell frequently reminds me of John Steinbeck, more of a political novelist than merely novelist. This dual need for a shouting voice and a gifted hand is echoed by Steinbeck who confessed in his The Grapes of Wrath diary that "Tractors," those symbol of destruction of the already downtrodden, must be "felt, heard" by his readers.

"Shift and Stack," 2019 by Anne Butler. "My working method is intrinsically connected to the act of making," writes Butler of her architectural pieces. The hand of the artist is not only present; it is dominant and inseparable from the aesthetics, Orwell would agree. Photograph by Anne Butler.

Orwell anchors his writerhood in an emotional attitude he acquired as a child, like comedian John Cleese, who brandished humor as a way to break the emotional hold of an overbearing mother, or children's author Roald Dahl, who, as a child, found writing as a form of freedom.

"We express our being by creating," wrote Rollo May, a sentiment that suits Orwell; it is hard to find anyone more genuine about his subject matter, like his eyewitness account of poverty.

Orwell credits his writing heft to a need to expose totalitarianism, promote democratic socialism, and elevate political writing to art and his starting point to a feeling of injustice.   In his own way, Orwell is saying his starting point is truth, or rather what is real to him. A writing disposition shared by both Ernest Hemingway and E. B. White.

Thank goodness he was lonely as a child.