Chess was the drosophila of AI - something one could study in detail and invent newer and newer approaches to solving it. It's no longer having that function, was surpassed by Go for a brief moment until that one got solved as well. A whole generation that was raised on this drosophila is slowly fading away, for the new entrants its no longer the game to beat, more like brain stimulating fun exercise/hobby and not something capturing imagination, telling us something about the very base of our intelligence anymore.

True, but the fun is currently derived from humans going up against humans as a sport. Machines are tools (for learning or cheating) but we are not interested in competition with them.

How will it work for math, where humans do useful work right now? I can not see battle math becoming a big thing, but maybe when some of the tedious stuff goes away math will be philosophy and poking the smarter system is where entertainment can be had?