The access roads to PBG aren't as good as BLI. Look at the map. Very few people on the east side of Lake Champlain would drive around the big lake and then cross at a very limited points just to get to PBG. So there are probably ferries, but I bet you they cost money.
Yep, ferries. 24 hours a day, depatures about every 8-10 minutes, $9 car and driver.
There are many small airports in the NY and some probably receive some sort of federal or local subsidy for air service. So they will have cheaper airfares and thus people wouldn't drive to PBG just to save a few dollars.
Then I guess these
wouldn't be those people that wouldn't spend a "measly dollar", right?
Oh, and people from Cornwall would probably drive to OGS, Massena, Norfolk or other airports instead of PBG, which seems to be more than an hour away on highways and not freeways.
Cornwall to Plattsburg is under 2 hours on roads that never have traffic jams. About the same amount of time as Seattle (part of that "significantly more" population than that around PBG) to BLI. Only that would be on I-5, notorious for delays all the way from Tacoma to Mount Vernon.
So if Cornwall is "out" then I guess Seattle is as well, which pretty much disposes of the population argument.