Why going “keyboard only” failed with too many websites, games and apps?

This really comes down to how and how well/mindful the website was put together.

Presently there's too much newfangled stuff that only the latest, with a few gigs of updates jammed up its rear, seems to display as intended, often with not even as much as if no javascript then ... Most of the newfangled stuff on the web I would not call mindful but that's me I guess.