Family. I can't convince my parents, and my wife's parents to pick up and move. I don't want to seperate my children from their grandparents.Where's the problem? It's not like the Free State is going to have a big stone wall built between it and the rest of the US.
You can still visit your parents anytime, and heck, they might move eventually too. They are targeting mostly young people without families and with a political axe to grind (like yours truly), or older idealists who haven't been compromised by life's jagged edges. They are not necessarily assuming that Joe America with a 4-person family and a home in Suburbia, IL is going to up and move to Vermont.
Also, a misunderstanding of the project is not that it's secessionist, more than it is about building a place where individual freedom is held in the highest regard (like it was when the US was founded). A goal is interoperability with the US, at least as far as it is compatible with what the US federal government has become. so, it's not like participants are going to have this invisible barrier between them and the outside world.
At least as far as I understand it 8)