I think it's because most people who switched to a mac did it because they believed it would be more stable (largely thanks to clever marketing). Since they already expect the mac to be better than Windows, that's what they notice, even though it's just different.

Also, the sort of people who use macs now either don't use Windows at all or only use it at work which means they're either comparing mac os to an old version of Windows or to an annoyingly locked down work version.