This reminds me of switching from Windows to Linux in the noughties: one of the complaints about Linux not being 'suitable for average users' was the lack of consistency between GTK/Gnome and Qt/KDE applications, and a lot of effort was spend on compatibility layers and such.

When I looked at a friend's Windows XP installation, it struck me that pretty much every application they used had a different UI system: WinAmp, Firefox, Opera, Windows Media Player, MSN Messenger, ...