If one strip employee wants to know another one go talk to them. An internal facebook will either be filled with corporate gibberish, empty, or cause someone to get fired.
Stripe (like many other mid-sized startups) is a distributed team with lots of remote members to any given member. Having an information oasis to help orchestrate "go talk to them" has value.
It's worth noting that they encourage talking in person, too:
> Outside Home, we encourage people to meet in person—one of our more structured approaches involves a chat bot that helps schedule lunches among Stripes who are least likely to know each other (more than 5,000 lunches have been facilitated since it was set up!).
How are you even supposed to talk to someone if you don't know who they are or that you should?