Because when you read about creators during say, the Renaissance, you don’t really have this much of a dichotomy. Da Vinci worked on a paid portrait project, and then did unpaid experiments on his own which ended up being useful for his paid projects. It was a very loop-like thing and I think he would find the explicit framing of “I’m doing this to make money” and “I’m doing this purely to create something I want to create” as alien. Ditto for most forms of art in most parts of the world, prior to the late 19th century.
The solution, I think, might be to focus primarily on the craft and not on the end product. You see this a lot with early 20th century fiction writers that moved in and out of journalism, with the idea that they were becoming better at the craft of writing, not at creating a final product or “being a good fiction writer.”