Well certainly no one moves there...except for me. Funny enough I was recently in Texas and thought that it would be a good place to move for work and cost of living.
I think mostly it's due to having grown up there. Most locals I know their ENTIRE family lives within 30 mins of them. Most people don't make a living. The amount of people on state aid is staggering up here.
So is tourism the biggest part of the economy?
Not as large as the anti-development crowd would have you think. Plus there are the eco-tourism and the regular tourists. The regular tourists hug the coast and spend all their money at shops and hotels. The eco-tourists are those that hunt/fish snowmobile etc... these are the ones that venture inland, but they don't bring tons of tourism dollars like the coast tourists do.
But like pgriz mentioned the tourism industry is mostly service based employment. These jobs are effected more greatly by economic shifts, poor weather and poor attendance. What Maine really needs is lots of manufacturing based jobs that pay more than state aid does.