Maine shares a lot of similarities with Vermont. The Portland area, where 40% of the population resides, is basically the only place in the state where you can transport a car for a reasonable rate, and the rate will still be fairly high. Any city not right off of interstate 95 will be next to impossible to ship to. Far north Maine is impossible to ship to.
Maine, like Vermont, mixes a small population with rarely traveled and mountainous roads. The only solution is to meet your driver. And since even transport to Portland can be difficult and expensive to arrange a lot of people prefer to meet in Boston. If you are shipping to Maine come ready to compromise.