If their art doesn’t make enough money then it’s clearly not in enough demand.

Unless you burden the word ‘enough’ with far too much work in that sentence, then that implication doesn’t necessarily follow. It is possible for something to be in great demand by those without money to spend. Furthermore, it is possible for there to be issues with the logistics between the source and the demand (e.g. demand is very physically distributed, or temporally limited and/or sporadic).

Money is a very particular way of empowering and aggregating only some demand. It ties the power of demand to history and not moral or egalitarian considerations for one.