This thought has occurred to me as well.
All accounts are on notice
But as to the why, it's anyone's guess. It feels like social engineering, where someone engages with a group of unsuspecting people hoping to compile a list of personal things some people might reveal about themselves, and compile it into a database.
There's two (possibly more) end goals:
1) Collect personal information to later attempt phishing and other potential account compromisation, like credit card accounts, bank account, etc. Remember those security questions that some of those sights ask like mother's maiden name? If you let information slip about who you are, and they look you up on social media, and learn that information. Easier to compromise now.
Other variations are to clone LinkedIn accounts, pretend to be you and connect with your coworkers, thus learning about your company.
2) Blackmail. This case had a pretty young "lady" in a room full of men. So you might get a catfishing situation, where messages are exchanged, maybe embarassing ones that you wouldn't want to get out. Once enough has been collected, then that person gets extorted.
There's likely other possible reasons, but it ultimately comes down to dirty ways to make money.
The fact that both accounts were doing this for 2 years really blows my mind. That's pretty hardcore.