For what it’s worth, a game like Diablo is one that I’d rather play myself than watch someone else play. But comparing an arguably single-player game to a competitive multiplayer game is a bit like apples and oranges. Games like CS invariably have more watchability because it’s more like a sport, not too far removed from something like football or baseball. People generally like watching contests, especially ones they themselves wouldn’t really be able to compete in. Like me! I’d rather watch someone else play games like that, the complete opposite of D4.
I think that as a game’s ‘skill check’ goes up, it also attracts more viewers for that reason. If it’s accessible enough, they’d probably rather play themselves instead of watching a ‘pro’ do it.
And finally, view counts on a streaming platform don’t necessarily line up with actual player activity levels either. There’s more nuance to it than that, as I somewhat highlighted above.