This is not HPC, they don't need to 100% use all cores.
If they knew how to do a state machine, a glorified chat app needs how many threads? Maybe 4: UI, network, audio, video. And the last 2 are only needed during calls.
They have 12 just because they don't know to do better.
Btw with teams (the application) off there's a com.microsoft.teams2.agent there anyway. What's it for, spyware?