Why is most of Maine undeveloped?

Black flies and gnats by the hundreds of billions.  Swamp, bogs and Moose.  Trolls and gnomes in the woods.  People that can't say their Rs.  Strange names like Molunkus, Meddybemps, Eggemoggin and Penobscot.

try being there in black fly season . 

Notwithstanding what you may have heard, I think there is a lot hazier explanation behind this. Listen to me. Dwarves. You've known about them, yet do you dread them? You ought to. I accept that the majority of Maine is lacking to give a territory to the awful dwarves of eastern United States.

Rustic land in Maine is very economical contrasted with more populated zones. A piece of the explanation is that there stays a bounty of the lacking area in Maine. Maine is the most forested state in the country.

Ever been to Maine? What's there? Not much. 

it is not always  active

Despite what you may have heard, I think there is a much darker reason for this. Hear me out. Gnomes. You've heard of them, but do you fear them? You should. I believe that most of Maine is undeveloped to provide a habitat for the vicious gnomes of eastern United States. Trump struck a pact with the gnomes to protect us, and we must allow them to keep their land. That, my friend, is why most of Maine is undeveloped. I hope this helps!

Akib

try being there in black fly season . 

Much of the land is unsuitable for economic development. It is not suitable for farming crops. Raising cattle is not economically viable given the feed lots in the Midwest. It does provide plenty of timber, which requires regrowth to sustain the industry.

There is nothing wrong with leaving land undeveloped. It is the natural result in this case of economic demand. With no industrial base and little land for agriculture it leaves a low population base with a small demand for additional housing.

The clue would be looking at an online map, and checking the names of the roads in most of the inland parts of the state.

Most are either logging roads, or they have no names at all.

No one developed the state (beyond accessing it for logging) because no one wanted to.