55MWs of power at half the cost of NextEra's standard offer rate

That has nothing to do with the corridor, it's a side deal made as incentive to approve the corridor, and for how long is 55MW going to last? 55MW appears to be an incredibly tiny fraction of Maine's yearly power usage. And there is nothing stopping them from making up the difference with a small rate increase that PUC will inevitably see no reason to not approve.

It's a small strip through incredibly rural woods.

It's not. Go look at the pics of existing parts of this grid. This is not the tiny corridor you may or may not drive through on your way to work each morning, this is a huge corridor. As proof of that they are actually widening the already existing parts of the corridor if the deal goes through, so when someone tells you for example, "It's actually only 50 miles of deforestation," it's not, because they have to widen the other hundred miles as well.