They used it to give away Teams to existing customers then force through price rises later by adding functionality behind additional licenses. They also leveraged Teams to sell a significant amount of conference room equipment that was running Skype Teams. Its likely Microsoft will start to use the embedded Teams usage to push up prices of their core M365 licenses, E3 and E5.
Its also heavily tied into Entra, Exchange, and SharePoint Online as its really three raccoons in a trench coat so its hard to fully use Teams without using those products, which must also be licensed, usually via a E3 or E5.
The timing of it being coincidentally when COVID hit meant everyone wanted a chat and meeting product, so good fortune paid a part as well. Also a lot of organizations wanted off Skype right around this period, so really fortunate timing.