Vienna used to be a really beautiful city....but it was also expensive as hell. The same goes for a lot of their other most highly rated cities. To me, cost of living is a huge factor in livability.
Oh....and nowadays Vienna is still expensive, but now its been infested with lots of muslims.
I should add....My criteria would include how good their roads are and how much parking space is available, how easy it is to shop and get the things I want anytime I want, etc. Note, pretty much every city they rank highly I would rank low and vice versa because I LIKE open space. I LIKE the convenience of being able to drive and not having to rely on public transport.