So non-employees join and provide free support to other users without having to pay them.

Why would anyone use Teams?

Same reason MS used a Perforce fork instead of Source Safe. Because the dogfood tastes terrible.

One of the executives at the late, great, Sun Microsystems once dunked hard on Microsoft by saying, "At Sun we don't make dogfood. We prefer to refer to it as, 'flying our own airplanes.'"

Dogfooding only works when the dog food is edible.

Microsoft employees largely use Macs, so no surprise.

Discord is owned by Microsoft IIRC.