Even if they were paying 10$ per user, it's basically the salary of one non-lower level engineer to have cross-company communication they are already used to.
It's the premise of paying your competitors money to do something that you already are doing. Someone manager probably got a bonus out of this move.
And corporate espionage is more prevalent than you may think. Can you absolutely guarantee 100% that the competitor, like Zoom in China, isn't sniffing their video traffic or recordings to some of their most sensitive internal business discussions?
Even if they were paying 10$ per user, it's basically the salary of one non-lower level engineer to have cross-company communication they are already used to.