Another way to think about it is that software that focus on performance loses market share to software that focuses on other things.
The average person will put up with a lot of friction to use something they're familiar with and needs a lot of incentive to change. If your thumbnails fail to load every 10000 times or every 100000th profile picture upload fails most people will just retry and hope it works the second time, not find a different service or app to use.