Their own fault really
The more you customise and move away from trunk, the more work you have to do. So when OEMs (and networks) pile on their own "added value", they make more work for themselves and start to bleat that upgrades are too much effort.
Well here's a startling concept. Sell phones with vanilla Android and let Google take the strain.
This is why iPhone remains superior. One OS, one variation, one set of updates. Not the dogs-dinner of semi usable effluent you find in the Android arena.
Windows Phone? Doesn't really matter, no sane person would use a MS phone.