Application developers often had a lot of crazy (and bad) ideas, but at least Windows itself was consistent. But then those crazy, bad ideas started affecting Microsoft, and then you could make the Windows Media Player look like eyeballs.
"Skinning" apps was a good idea in theory, but in practice, it never offered anything better than the default of Windows 2000 and earlier eras. Now you can't change anything in the Windows UI except a few colors.