You're left off with XAMPP and OpenSource tech?
At a previous job the building next door was a remote office for a non-IT part of a large non-tech company. They spent the money to get some kind of carrier line (maybe EPL/EVPL?) solely for teleconferencing.
While the system is almost certainly not difficult to compromise for TLAs and others, they get assurance that the data hasn't left "their" network,
I personally don't think there's much rhyme or reason to that particular permutation of those policies, but there is certainly a large group of buyers who are fine with potentially backdoored commercial products as long as "the data doesn't leave our network" and hence would not be OK with Google's solution.
We've only hit this limit with very large all-hands meetings or presentations that lots of people also want to dial into. We often have a separate view-only stream for those cases.
Though, I believe both Webex and GoToMeeting charge extra to have this ability.