E2E is something nerds complain about.
It’s a hard problem, which gets much easier and delivers a better UX if you can trust the service provider. Also consider why you trust 70 meeting participants more than Zoom/Microsoft/Google/Verizon?
For the very simple reason that "the people that I choose to communicate with are people that I have chosen to communicate with", whereas the communication medium chosen is "the least-bad available". I am able to take whatever other measures I wish via other channels to verify and built-trust-in the participants, but I cannot do so with the communication medium owner.
You would play it similar to how you attend a Zoom meeting. They could probably reuse most of the client code for this feature. But yes, I agree this is likely not the user experience that most users want.