Wayne Williams at Betanews has a more detailed answer, though:
It’s easy to understand why Microsoft took the decision to take Windows 8 in a new direction. PC sales were falling, and people were transitioning to iPhone, iPad, and Android devices. Microsoft felt it needed to do something radical to remain relevant in this changing world, and an operating system that could run on PCs, tablets, and smartphones seemed like a smart move.
The problem, of course, is the Start menu-less Windows 8 was too radical an approach for PC owners -- the bulk of Windows users -- and the OS itself was simply too half baked. There were too few decent non-PC devices around, and Microsoft had to build a Windows Store from scratch -- not easy.
Fast forward to 2015, and Microsoft brings out Windows 10. On paper, this had everything going for it. It was replacing a disliked predecessor, it offered what seemed like the best features of Windows 8.x combined with the best features of Windows 7, and it was free. What was not to like? Plus, like Windows 8.x, it could run on PCs, tablets and phones.
But Windows 10 hasn’t been the sure fire hit it was expected to be. It will be on 1 billion devices by 2018, Microsoft crowed. But even forcing users to upgrade to it didn’t get the OS any nearer to hitting that magical number. Windows 10 has a market share of around 25 percent now, which isn’t bad, except that’s half of what Windows 7 has, and people have stopped upgrading.
Williams then goes on to discuss why people have stopped upgrading in more detail, basically boiling it down to two main issues.
First, and apparently foremost, is Windows 10's focus on apps:
And here’s the biggest problem with apps -- they’re now universal, and designed to run on any device running Windows -- PCs, tablets, smartphones -- but who has a Windows smartphone these days? Pretty much no one. The whole point of Universal Windows Platform (UWP) apps is you can install them on any Windows device you own, but if you only own a PC they why would you want to install an app when you could install a more powerful program, and enjoy greater choice?
Second, mentioned only in passing, is the non-stop advertising:
The main issue people are -- rightly -- hating on in Windows 10 at the moment is the adverts that Microsoft has peppered the OS with. These, for the most part, are to push apps, but I doubt the Windows Store has enjoyed a huge uptick in downloads as a result of them -- it’s just another annoyance Windows 10 users have to put up with.
Weirdly, Williams spends several paragraphs discussing the problem of apps, and only one talking about the adverts. Yes, both the Universal Windows Platform's anti-consumer approach, and the relentless drive by to monetize their Windows user base in any way they possibly can, are problems. But I think they miss the point, somewhat. These things are problematic, in and of themselves, but they're not the root of the problems; they're symptoms of more serious underlying issues.
Microsoft's entire approach to a Windows user base that has thrived on choice and freedom is to limit choices wherever possible, and coerce users when they can into behaving in ways that benefit Microsoft as a corporate entity. Only when the backlash has proved too intense has Microsoft backed off on these two strategic imperatives, and they never back off for long.
That's why the Creators Update will once again include a setting that allows users to block the installation of Win32 software -- something which has been built into Windows 10 from the beginning, and which was initially turned on by default until the PR backlash forced Microsoft to back down.
That's why the Creators Update will once again be auto-downloading itself, even over metered connections, long after Microsoft apologized for doing that, and appeared to reverse course, after terrible PR forced them to admit that there were problems with the practice they hadn't considered. Apparently, they've reconsidered, and now think the practice is just fine. This, in an update which also allows users to postpone restarting after updates are installed, something else they had to implement because of terrible PR.
The major underlying issues here are trust, and choice. When Microsoft altered the behaviour of the "close window" button to force Windows 10 upgrades, it undermined trust, just as discovering that Windows 10 includes a built-in keylogger, again enabled by default, undermines trust.
Removing the option to disable Cortana, even though Cortana monitors everything the user does and uses cloud-based services to perform even local hard drive searches, limits choice and undermines trust, as does locking Cortana to Edge and Bing, a combination of software and service that the market has resolutely refused to use when offered the choice.
Pushing ads through the OS, a behaviour that's seen in no other operating system, undermines trust, even as it attempts to influence users' choices.
Every time Microsoft denies security updates to people running Windows 7 on 6th generation SkyLake CPUs, it undermines both choice and trust... choice, because people who've bought and paid for Windows 7 explicitly have the right to run it on any one PC of their choosing, and trust, because Microsoft are now violating that agreement to unilaterally force users onto a new product that those users have repeatedly refused.
This is why people aren't switching to Windows 10 anymore, even though they can still do so for free, something which we're all supposed to pretend is some sort of secret even through everybody already knows who cares to know. They don't trust Microsoft to treat them and their choices with any kind of respect at all; they don't trust Microsoft not to spy on them; they don't trust Microsoft to keep their own given word. Darth Microsoft have altered the deal one too many times, now, going back to bad practices again and again, for anything they say to be believable anymore.
Does Microsoft need to rethink their Windows 10 strategy? Yes. Yes, they do. Desperately. Now would be a good time; in fact, they may already have left it too late.
They need to change course, here. But will they? Probably not unless and until they're forced to.