Yeah, there's definitely a stingy factor to it. To make matters worse, since your game is about furries, furry artists tend to infamously be even more stingy about the protection of their art or even their character ideas even if it's a non-descript anthro raccoon that happens to be fast. The subject matter of the game as such, makes the chances worse for Free art. Nothing you can do about it for that, though. You'd get more submissions of recolored fan characters with "original character do not steal" rather than genuine new artwork from someone who knows even what the brief summary of the GPL license is all about

I'd say the era of generous art hobbyist died around 2005, when Garry's Mod and Source this source that became a magnet of them. I know it explains all those free shooters from that year not looking better or having much new art at all by now.