Users don't care because Teams still basically functions and the performance problems are at most a minor inconvenience. As a result, organizations don't care because Teams is cheap and does everything they need it to. As a result, Microsoft doesn't care because dedicating dev resources to something which neither saves them money nor attracts more customers is a waste.
Microsoft employs many smart people and I'm sure Teams' performance could be improved by orders of magnitude if they wanted to. But why would they want to?
(And to reinforce my point, when the performance _did_ get so bad that people apparently actually started caring, Microsoft not only improved it but made a video advertising it. It's just that there's no incentive to optimize any further than is necessary.)