This would be understandable if it happened quickly but normally Teams has a seizure for a minute or two when you try to join the call and then you get told to sign in. Whoever allowed this behavior to ship should be fired out a cannon... when I click join a call, absolutely nothing should stop me from joining a call.
In fairness this might not be explicitly Teams' fault. It's built on top of a terrible authentication platform which also seems to be down at least four or five days a year. 365 is one of those things that could not exist if not for the incredible monopoly Microsoft has over Excel.