I'm a meetup organizer and sometimes get this but the other way. People insist that our current platform is not appropriate or inclusive because it requires an email signup, or the group chat is on a Meta-owned platform, or whatever. Who are you to say that your opinion on what's inclusive or not is correct? Choose something other than Facebook and you'll get others saying you're not inclusive because you're not there.
No one has "bizarre insistence" on use of social media, they're just there and it's the easiest option for all parties. People like you and me are the ones who are perceived as the ones bizarrely insistent on not being on social media. This doesn't make it wrong, and it's luckily slowly becoming more and more accepted, but it is important to keep in mind.
You are right that ideally groups like these should cater to all audiences but that's a lot of effort, and many organizers do it on a voluntary basis, not as a job. In my case, I know that 98% of people are included in the media that I use for my audience, and catering to the last 2% would double my workload. Not happening.
Since as far as I know, an E-mail address is required in order to sign up for Facebook and other social media, E-mail users must be a strict superset of Facebook users. It is clearly more inclusive of people.
As far as workload goes, we have not found anything lighter weight and less maintenance than an E-mail list.
No one has "bizarre insistence" on use of social media, they're just there and it's the easiest option for all parties. People like you and me are the ones who are perceived as the ones bizarrely insistent on not being on social media. This doesn't make it wrong, and it's luckily slowly becoming more and more accepted, but it is important to keep in mind.
You are right that ideally groups like these should cater to all audiences but that's a lot of effort, and many organizers do it on a voluntary basis, not as a job. In my case, I know that 98% of people are included in the media that I use for my audience, and catering to the last 2% would double my workload. Not happening.