This is expected. As the parent comment said, it's common for people to be "too lazy" to unsubscribe from meetup groups. It cost nothing to be a member (though I understand that group owners are charged a fee based on the number of members), and I don't think that most people like clicking "unsubscribe" from anything. It's some kind of Thinking Fast and Slow mind trick involving familiarity and the fear of missing out, or something.

For a lot of people, meetup group emails are like a newsletter or an rss feed. They might skim it occasionally, but rarely go through the trouble of actually showing up. So, it's not you, it's them. It's probably best to see it as "I have a meetup group with 10 people in it", which is an accomplishment on its own.