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.