If you don't have Teams yet, you are either in another rollout, you have done something to prevent it or your PC is managed by someone who have prevented it somehow. I think that covers all.
As for why I only use Windows now and then and since I have had a habit of supporting others I keep my personal Windows PCs as plain as possible so I can see what others suffer (obviously I remove nagware like McAfee and make sure spyware like Chrome isn't set as default browser but I have gone as far as to voluntarily run my PC with Norwegian language).
It is a bit tongue in cheek (since I am Norwegian) but only a bit since it is an extra hassle to try to mentally translate what translaters read in English when they created the unsearchable phrases that show up in a localized Windows version.
Teams is not default in Windows (at least my install) - I don't have it and when I have to do meetings in Teams and I am on my Windows machine I just open the meeting in Chrome.