It's all about framing though isn't it? If Uber were '1 (miserably below expectations) .. 3 (met expectations) .. 5 (above and beyond)', you wouldn't see that.
It doesn't really matter as long as everyone's on the same page I suppose. Sure, you clip stuff off the end.. but doesn't everyone just want a taxi that gets them A-B without problem? Who's actively seeking 'above and beyond'? Maybe 'would've scored >5 if I had them' is not a problem, because nobody cares?
(I should maybe say I've never actually used Uber!)
The opposite is uber where rating affects future service and puts a lot of power over others in your hand. Not giving 5 is socially unacceptable like not tipping vs tipping less and complaining.