When large MMO guilds have had a mostly trouble free chat client that supports a few thousand concurrent users on the free time and good will of admins I'm loathe to believe that this shit is impossible
For example, large MMO guilds have a quite different regulatory environment from, say, a large healthcare organization in the US governed by HIPAA. It's an extreme example, sure, but a homegrown, dumbed down solution, might be the only way to ensure regulatory compliance.
It doesn't take a lot of imagination to come up with other scenarios. I can't defend Uber doing it because I'm not involved, but large MMO guilds are not archetypal of enterprise systems.