Oscar Wilde made this point in this letter from 1890, right around the time he was achieving success:
The best work in literature is always done by those who do not depend on it for their daily bread and the highest form of literature, Poetry, brings no wealth to the singer.
It’s great to not have a day job in some ways. Your whole day can be spent writing, nobody keeps track of your coffee breaks. And so on. But sometimes it can be nice to write for the thing itself, and not because the electricity bill is due.