Microsoft replaced the fully functional Win 7 with the gobsmackingly unusable Win 8. Not a good way to create love and support in the population.
They replaced that with 8.1, because they had to, but didn't make it friendly enough to win people back.
Then when they brought out Windows 10 they managed to keep some pretty nasty bits of usability, like turning the control panel into a mish mash of different interfaces with some controls inside places you wouldn't expect to find them and others so well hidden you're more likely to find a Pokemon. Or the Start menu that is full of unremovable "apps" that you might never want, and programme links (some that you'd never directly launch, like PDF readers) that are installed within folders of crap that an ordinary user would never be able find and (re)move.
But in case that wasn't enough to put users off they then went to massive lengths to force this on to users with Win 7+. (OK if it was just Win 8.x they might have a case).
Meanwhile, they just didn't try to market the phones in any sensible way. Neither in advertising nor in range ( cheap or expensive with nothing between). Maybe because they had lost interest and wanted to flog Tablets instead. Since, "it's not a popular OS with vendors," they needed to get the public onboard directly, but couldn't be arsed. It's a great phone. It doesn't have Apple Tax. It isn't an outpost of the Google advertising agency. It is very usable. But now it's tarnished by both the Win10 debacle and the taint of failure.