I know of no other place where it is so easy to gather people. Just post a new event and people will notice and sign up.
If you switch to a self-hosted solution you will have to find an audience through other channels. Which, for many Meetups, is quite the challenge. Remember "build it and they will come"? Same applies to events. "Set a date and they will come" - doesn't work that way unless you have an existing audience.
Personally I don't mind paying 2$ to attend a meetup. The old/existing pricing model seemed much smarter for everyone involved though. Organizers pay to get access to the audience. The audience pays nothing so that the audience, the real value, can be maximized. I hope that they won't destroy their value with this move...