Supply is certainly a factor, but it's only one factor. There are plenty of would-be Van Goghs dying penniless today that will remain unknown and forgotten. What matters is desirability; Van Gogh's life story and the fact that his work went unnoticed until he was already dead, and now everyone knows who he is, certainly makes his work desirable.
In a modern age where anyone can pick up a brush and get $20 of paint from a Michaels, and internet has made fame a very different beast while offering infinite things to compete for our attentions, the path to success is going to be different for anyone trying to make a name for themselves. And most artists would prefer to be successful while they're still alive. It ends up being very much more about who you know and how you can market yourself than how "talented" you are, and talents is in quotes because it's less about technical skill or even "creativity" and more about being able to make yourself stand out or make what people want to buy. There are controversies and plenty of articles discussing the power and influence gallery owners have over what names end up being "known" in the art world, and how it's all a laundering/tax fraud scheme/racket now, but that's beyond the scope of this thread imo.