When someone decides to start a meetup, they usually have some personal reason for doing so. The standard model is the same as the standard model for online social networking. You make something, you encourage people to come along and use what you have and then you find a way of monetising what people are doing there.
Which is fine.
But it treats the majority of people in the room as a resource. Nobody likes to just be a resource, they see themselves as useful but also they want to get something from the people in the room. So why not let them? Many first-time meetup organisers think that it's all about them. They see themselves as a central node in the network and all they care about is the connections between themselves and each person who turns up. This is natural, everyone does this - and that's the trouble - all the people who have come along see themselves as a central node and only care about the connections between themselves and everyone else.
So meetup organisers need to see the extra value in all of this. Take the focus off finding success through having 100 people in the room and look instead at how many potential connections are actually being made and whether anything's coming from those connections. The number of connections increases geometrically as the number of people increases and everyone gets value from making new connections or enriching those that they've already created for themselves. Make space for people to truly connect and then see what's in it for you.