Its also the best new piece of big software out there. In the days before teams, remote working together in an entire company was hell. Either you were on skype for business, or each team had their own thing that was different and not official.
With teams, everyone is on there. The other microsoft things are integrated, not seamlessly because of bugs, but easily good enough for most things. The chat is available and used, and a nice alternative to e-mail for smaller things.
Teams works well enough for most people, and is very easy to get started with. So most people actually use it, and you get a network effect.