I have two competing hypotheses for it. One, they're just bored, and LinkedIn is the new Facebook for middle/upper-middle class people. Two, there are signalling to and chasing people with access to lots of money, who for reasons unfathomable to me, also hang out on LinkedIn.
I think the "middle-class" comes from the fact that such people have cash savings to weather a job hunt, whereas people without savings have to start working pronto on whatever if they're going to be eating and roofed in two weeks.
Here's a third one: It's curated to folks with similar professional interests and isn't political.
People receive a lot of BS on Linkedin but for some people it works. This being said, the people I know whit 8-9 fig net worth, you wont find on linkedin.