If people wanted to see someone's skill at games like chess, it wouldn't be too difficult. There are plenty of historical pre-cursors to modern chess (like courier chess) or regional variations (Chinese chess). All of these are/were pretty well regarded. And that's not even getting into modern, intentionally created chess variants (like Chess960 that you mentioned). Picking a random version of chess would shake things up and force players to think on the fly.

But people who enjoy modern Western international chess seem to want to see that one single version of the game optimized. Which is fine, I suppose. Though it would be nice if we saw more alternatives (granted, there are currently some popular alternatives like blitz chess).