I think one factor is that Google is very nebulous. Facebook's and Uber's ambitions are pretty obvious and easy to understand. Google is a search company and an advertising company, but it is also a social network and a cloud storage provider and a thousand other things. And some of its products aren't even gratuitously Google-branded (e.g. YouTube -- even if it's more integrated into Google+ now).

Sure, there is a vague awareness that Google is invading your privacy and harvesting your data, but it does so for "free" and generally makes it look like a good deal. It's also a lot more subtle about it than Facebook.

Google isn't morally superior. It's just less obviously evil. And let's be honest: to the average bloke (even on HN), the problems with Uber or Airbnb are a lot easier to relate to than the much fuzzier problems with Google (privacy, media licensing, etc).