Teams is a heavyweight behemoth with awful UX while Skype orginally had a very lightweight feel to it. Of course, Microsoft had to kill that through various UI "improvements".

Also, Skype has an official Linux client.

Instead of developing Teams (NIH at its best), they could have carefully developed Skype into a similar platform. But I'm not sure a giant like Microsoft is capable of something like this. But at least their 8.5bn investment wouldn't have been just to kill a competitor.