Because LinkedIn makes your employment front and center it encourages status games .
The way to understand LinkedIn is no one is actually trying to engage in good faith. Everyone is seeking status points in a game they're playing. And that status depends on their endowment (people they know, institutions they are part of)
Status conferred from their boss, their peers, their underlings, people in similar roles - It's why LinkedIn feels like a lot of thought-leadering, because the only way to get status is to post something that gets likes within the status game you are playing
Forums like this one and even to some extent Twitter are more evolutionary in that you will likely see higher quality ideas get conferred status.
I use LinkedIn (getting traction for my product). I don't enjoy it but I do understand the game being played.