My Grandma doesn't have a need for backwards compatibility or the million other things that stop Apple from just making a new operating system.
Normal people's use cases for their computer is light file management, light document and productivity workflows and everything else is done in the browser. Hell, most of the document processing and productivity crap is in the browser these days too.
This is the real answer - 90% of people can use a phone or an iPad for their general computational needs - and the PC/Mac itself will trend toward that, with harder and harder gates to bypass to get a truly "general" computer.
Normal people's use cases for their computer is light file management, light document and productivity workflows and everything else is done in the browser. Hell, most of the document processing and productivity crap is in the browser these days too.