I'd like to know the same about Win 10. I have been using it on five computers since it came out and haven't had a moment's trouble with it.
Win8 introduced a user interface style "Metro" which was very poorly accepted by Windows users. It was very different in ways that caused confusion, frustration, and massive amounts of lost productivity. Microsoft ballyhooed it as a great new thing but it was unwelcome and for the most part it only was bought on new machines where it was forced on the buyer. Very few XP or Win7 users upgraded voluntarily and stayed with it.
Win8.1 fixed a few of the most egregious errors, most Win8 machines could be upgraded to 8.1, and at this point the only people running plain Win8 are the ones whose machines failed to upgrade.
A lot of Win8.x users rolled back to Win7. The rest migrated forward to Win10 when it came out. Win10 stayed with much of the user interface, but Microsoft ate some crow and re-introduced some of the important, useful features it had removed in Win8.x
Now, all that said, was the underlying operating system itself bad? Not at all. The problems were all in the GUI, the user interface.
And of course, there are a number of folks who use and like Win8.1. More power to them -- ain't freedom of choice great? They have until 2023 to be getting security updates, before they have to migrate to Win10.