People like wallpaper...
Microsoft tried to make it (albeit to late) so that a wallpaper image could be seen through the tiles but by that time, it was too little to late. There wasn't enough interest in Windows Phone to right that ship. This theory of mine doesn't specifically blame this one detail for the ship wreck that was Windows Phone. The main reason it tanked was because there were not any apps for it. That old catch 22 of you need people's interest so the developers will have a reason to build apps, but you need apps to gain people's interest, was the number one reason it all fell apart.
When ChromeOS and the first Chromebooks came out, you turned them on to the browser. Windows and Mac people bitched and complained because they had no "desktop." What the fuck did one need with a desktop though?" For ChromeOS, everything is cloud based or stored in your limited files. Google ended up caving in and quickly created a desktop that could show off wallpaper. It still does absolutely nothing. Serves no purpose other than being a place to display wallpaper you never see because your browser is almost always open. People bitched less after that though because they had their wallpaper.
It seems kind of stupid as to what people get stuck on. Completely non-essential things with little meaning but create massive stress. This seems to be the way of life in general. Millions of people scurrying around with purpose but have no real purpose. Meaning but no real meaning. We just do what we do because it is what we do. We obsess over the stupidest things and find value in convolution. Yes, we humans are fucking weird.
I also get that we do this for green paper so that we can survive. It's still not a "real" purpose outside of that though.