I imagine that at least one factor there is that building up is prohibited by zoning—a super brief glance at Concord's zoning map & code it looks like the only kind of residential buildings you can build anywhere without special permission are single-family.
Now there are surely people living there who would argue that this zoning has protected the shape and nature of the town they that they prefer, but the flip side of that coin is that, at $1.4m, a median home in Concord costs more than 3x that of the country overall.
There's probably some truth in that. On the other hand, Concord is a pretty far-flung suburb; you're probably over 30 minutes to get to Cambridge without heavy traffic. I believe the prison out there is closed now but don't know what the plans are for the land.
Sure, I wouldn't imagine it'd turn into a cluster of skyscrapers if the restrictions were not there, but I would imagine there might be some small apartment buildings near the train station. New Jersey has had some impressive housing changes happen by opening areas near transit to development in not-dissimilar environments.
Apparently, the governor is interested in using it for housing development but I'm sure that will be tied up in the courts for years--especially with it being Concord.
Now there are surely people living there who would argue that this zoning has protected the shape and nature of the town they that they prefer, but the flip side of that coin is that, at $1.4m, a median home in Concord costs more than 3x that of the country overall.