Do you think they filled the homepage and the feeds with completely random content?

Of course. You have to start somewhere. In order to attract you create the lowest barriers. Like a wild west atmosphere. In the beginning, everything is welcomed. If you restrict it/complicate it too much people won't come.

You don't get users by showing them loads of spam.

I did not talk about spam. I talk about "junk" or "shit posts", random stuff. People like cats, tits, cutsies, you name it.