Earlier quoted context omitted.
This is why Facebook ended up being the tool of choice. Stay in one app instead of logging into 2 and checking your email and a website. I'm only surprised that 1-3 can't all be done via Meetup.
They all can be done through Meetup - I think the point here is that multiple channels avoids vendor lock-in and increases the likelihood that a user will overlap with one of the 4 communication strategies.
The email list is probably the single most important part of the tech stack actually.