Pretty sure this is due to people abusing the previous system for CSAM-type stuff:

Earlier this year we saw an increase in the number of reports we received about some people using our service in ways that we cannot tolerate. To be more clear, this was not about some people merely saying things that others disliked.

Over the past several months we tried multiple strategies in order to end the violations of our terms of service. However in the end, we determined that requiring authentication was a necessary step to continue operating meet.jit.si.