Charlie Demerjian from SemiAccurate wrote a great article about Windows 8 and Windows RT's glaring problems, that most other tech sites avoid talking about. It's a long post, so I'll try to make a summary out of it, while adding some of my own thoughts.
#1 Windows 8/RT Are Bloated
To put it bluntly, both Windows 8 and Windows RT simply can't be considered "mobile" operating systems. They have way too much cruft and legacy code that impacts not only the storage of the device, needing an order of magnitude more storage than Android and iOS (combined), but it also makes it much slower on the exact same hardware. Jelly Bean on Nexus 7's lower-clocked Tegra 3 was much faster than Windows RT on the Surface.
The same thing is true for Windows 8 and Intel Atom, which is in the range of Tegra 3 and other ARM chips in terms of performance, but it's still way too slow to handle Windows 8. Atom has improved slightly since the netbook era, and we used to think of netbooks as very low-end and slow machines. Windows 8 might throw some animations here and there to make it "seem" a bit faster, but you still waste just as much time on the tasks and operations you want to do in Windows 8. Windows 8/RT hybrids are just netbooks with touchscreen that cost twice as much.
#2 Too Expensive
What I said above actually means that either for the same performance you get to use a Windows 8/RT operating system that is much slower than the competition, or you need to throw much faster hardware at it to put it in line with the competition. And much faster hardware also means much higher prices.
To make matters worse, Microsoft is actually charging manufacturers $90 for the Windows RT license, and up to $200 for Windows 8 Pro. As you can imagine that puts a huge burden on OEM's to compete not just with other Android-based devices, but with iPads, too.
Try to get a manufacturer to make a "clone" of the iPad with the exact same quality materials, same "retina" resolution and quality screen, the same fast performance, and the same (free) storage, and they won't be able to sell it for $500. They would need to use a $200 Intel Core processor, a much bigger (and more expensive) battery (which would make the device thicker, too), just to get in the same performance range (how fast it feels, not what the benchmarks say). And then add the $90+ they have to pay for the license. They won't be able to do it. The closest you see today is some $700 Core i3 tablet with low resolution and significantly worse display and build materials.
They can't match the device spec per spec, nor can they match the price. Of course, it's even worse when compared to the Android side, where manufacturers don't get the huge profit margins Apple is getting on the iPad, and they can lower the price even more. And Android costs them nothing. In fact they even make some money from Google.
Remember when Microsoft promised 100,000 Windows 8 store apps within 90 days of Windows 8 launch? That never happened. Instead they only reached half of that goal, after twice the amount of time had passed. If this is any measure of Windows 8's success, that would put it 4x behind Microsoft's expectations for Windows 8. And that was with Microsoft paying a ton of money to developers early on to get them to write apps for the store. Microsoft was basically hiring freelancers for their stores at that point.
But it gets worse. Recently Microsoft announced that it's only going to pay $100 to new developers. That barely covers a small fraction of the price for Visual Studio, let alone the development time the app developers would need to invest to make any sort of decent Windows 8 app. In the meantime Eclipse is free, and Xcode for iOS costs a few bucks. So the Windows 8 ecosystem is only going to remain behind Android and iOS from now on, because even Microsoft can't afford to basically hire freelancers for their store.
These are three of the main reasons why both Windows 8 and Windows RT are on a death spiral for Microsoft, because those 3 reasons are why Windows 8 and Windows RT can't become competitive in the mobile space. This is also why manufacturers like HP, Acer, Dell and Samsung are starting to bail out on Microsoft.
HP has become visibly bullish with Android and Chrome OS ever since Microsoft announced Surface last year. Acer, Dell and Samsung have all expressed discontent with Windows 8, Windows RT and WP8, while turning more towards Chrome OS or Ubuntu (in Dell's case). And Samsung, of course, is doing very well with Android, anyway. My guess is that once Tizen is launched, they're done with WP8, too, since why would they ever need an "alternative to Android" that is selling so poorly, and is completely proprietary to Microsoft, and have no control over it?
Things are definitely not looking good for Microsoft, and I doubt the service pack they are going to launch for Windows 8 this year (the Windows 8.1 update) will make any difference in all of these. Now, do head over to the SemiAccurate article for more insights into why Windows 8/RT is on a death spiral.