Meetup has a messaging system so they don't have to give out email addresses.

Anecdotal: I never enter my email address on meetup group registrations because it seems weird that they would ask for it since they can already message me. I think it's also because so many organizers have abused meetup.com groups and meetup.com itself, despite millions of users, looks shady.

I always enter my email address on an Eventbrite event though.