Even though they provide several services - social network, jobs (for hiring managers and jobseekers), learning etc., none of them really have any tight integration with each other and can easily exist as separate services.
The website and apps are clunky and slow to load and has tons of dark patterns (contacts upload, profile visit tracking, everything over-shared by default, email blast when you sign-up etc.). I have heard LinkedIn hires lot of bright people and pays them quite well - but why their product still sucks?
Because engineers don't make decisions. Managers do. It doesn't matter if you have the smartest engineers in the universe, if you're still going to incentivise managers with dark patterns.
I never post anything but when applying for a new job you can't really do without. A HR rep will not blink twice if you're not on Facebook. But no LinkedIn? They just won't take you seriously or think you have something to hide.