I do think it's likely more passive than active. People at Google aren't deviously plotting to hide buttons from the user. But what is happening is that when these designs get reviewed, nobody is pushing back - when someone says "but how will the user know to do that?", it doesn't get listend to. Instead the people responsible are signing off on it saying, "it's OK, they will just learn that, once they get to know it, then it will be OK". It's all passive but it's based on an implicit assumption that uses are staying around and optimising for the ones that do, making it harder for the ones that want to come and go or stop in temporarily.
Once three or four big companies start doing it, everybody else cargo cults it and before you know it, it looks like fashion and GNOME is doing it too.