Because adding brains and storage to hardware is expensive. And putting simple things on customer prem means less things can go horribly wrong.

And people actually like controlling their hardware from out-of-the-home, which makes doing everything locally even more complicated.

When you start trying to present end-users with a graph of whatever metric you want, you run into issues with storage, response time, CPU usage, storage, the web front-end, storage, etc. Then you have issues updating all that.

And if you want to do something like, say, comparing and benchmarking against other users you can't.

Really, only technical people care about this kind of stuff, and they can go ahead and write their own or use HA.