From my experience that kinda makes it worse because constantly people will say "X has this now this add that" and it's normally a case of "Well that's a ton of work to do because we did Y".

Does the fork stay current with upstream?

It takes 1 person a few percent of their time to manage something like that for internal use only. And you still get the gains of keeping secrets internal and cost savings on licensing costs which might actually pay for a good chunk of the effort in the case of running an existing service.

Compare with a small development team for a significant percentage of their time to build a halfway decent chat tool.

Miles of difference.