What changed is FB had to make money - and they discovered "outrage" sells. That's the full answer. It has nothing to do with the lower-class crowding up your social network lol.
The "grow fast monetize later" model that social media companies use, along with the user being the product, inevitably acts as a template for bait and switch.
All degradation of user experience stems from that. Of course using a social media platform during its "growth phase" is going to be a lot more of a pleasant experience than using that same platform when it's trying to maximize revenue.
It's no surprise that Facebook also seemed to chase the golden goose, but now that the main page is nothing but outrage or divisive news people are leaving in droves because they're fed up with seeing the same, day after day.