Others have mentioned that this is almost certainly the result of a long course of A/B testing. The problem with this kind of aggressive A/B testing is that it's a game of "how far can we push the user?" So instead of having enthusiastic fans, they have people who begrudgingly use them. Sure, Google picks up an extra nickel here or there, and I'm sure some PMs got a raise. But I don't know any strong Google boosters…
Google also does this with Chrome. Users are subjected to "field trials". No explicit consent is requested. Most users are probably unaware. While it is possible to see which trials one is a part of, Google is not transparent about what exactly these trials entail.
https://www.ghacks.net/2013/04/05/field-trials-in-chrome-how...
https://textslashplain.com/2017/10/18/chrome-field-trials/
https://chromium.googlesource.com/chromium/src/+/master/test...
https://blog.chromium.org/2012/05/changes-to-field-trials-in...