Yeah, Black Rock is relatively cheap. But it's Bridgeport, arguably the poorest and least desirable city in CT. Probably Hartford is the only "competitor" in the state re. reputation. So most won't consider it.
But I agree, Black Rock is pretty nice. Urban, walkable, and attractive coast. The same coastal RE in Fairfield, CT, right next store, would be 4x the price. In Westport, the next town over, at least 5x the price. Even crazier closer in to NYC, in Greenwich and Darien.
Looks like a nice Black Rock home is around 400k these days, still insanely cheap for Fairfield County coastal neighborhood:
https://www.zillow.com/black-rock-bridgeport-ct/
Also, there's a major new Metro North station very close to Black Rock, on the Fairfield side. It's called Fairfield Metro, and has very high service frequency, as well as express service to Grand Central.