This happens because of how Microsoft approaches product development and design. On many product teams, PMs end up doing not only the product design decisions but even designs much of the products themselves. This works for them because it focuses product cycles on releasing what "matters" to the customer, but it ends up cutting craft and quality. This makes their products poor to use, but is also what drives revenue…
I suggest that Teams only gets used because it’s included in the enormous license that companies buy for Exchange and/or Office and the most popular alternative has its own fees. Large companies don’t want to fork over another licensing fee in the tens of thousands of dollars for Slack when they’re getting Teams “free.”
I think it also has to do with how much money Microsoft is kicking back to the right people in those companies to evangelize Microsoft despite knowing that it sucks.