Group chats are basically the Circles that Google+ saw the need for but could never get fully set up. A lot of people don’t want to share personal updates and photos to a broad swath of friends and acquaintances.
Meanwhile Instagram and Facebook keep evolving. Facebook is turning into a weird Reddit for older people. Instagram is turning into a hipper LinkedIn, where artists, musicians, and local businesses share career and business updates and advertise their wares.
No LinkedIn, not you, you boring Ted Talk humblebrag.
I doubt many are being serious.
Business culture (at least in the US) is so steeped in lying and general fake-ness that in-group signaling as "real business person" involves public performances of bullshit.
It's what you're supposed to do in interviews: bullshit just the right way, to show you understand the game and are willing to debase yourself to play it. Otherwise you're "risky", either due to excessive commitment to ethical principles or to being too clueless or inept to play the game right. That's what's going on, on LinkedIn. "Humility" and "realness" even have to be faked just the right way.
It's incredibly gross.