The protocol we have always implicitly used in this case is 'no news is good news'. I.e., participants in the meetup understand that they only have to communicate 'I won't/can't be there.' The reason is optional. Could be lots of things.

But socially this has gotten inverted.

I have several very long relationships with people (>30 years) who are overwhelmed by this. Living their lives immersed in constantly buzzing irrelevant social noise.