Algorithm-based social media "recommendations" has normalized us putting up with blatant SPAM
Unfortunately you weren't far from the truth on that second part about Gmail showing ads in your Inbox.
https://insightinvasion.com/gmail-ads-users-frustrate-as-google-tests-ads/
Not sure if they are still testing this out on people. I know I never got put into the group of users they tested it on but I'm at a point now where I don't trust it won't be pushed onto people sooner rather than never.