VM aren't BT. Whether there are 1,400 or 14,000 residents in a place if they have fibre running through it it'll have the same kind of viability. Most companies have to dig ducts passing each home to deliver broadband services and population density is more important. Villages can be among the cheapest places to deploy new network and only become a problem either when long fibre runs are required to reach them, or using a legacy FTTC solution.
Holywood's network would've probably been built by one of VM's predecessors that may or may not have had the franchise for Bangor.
The build in Bangor is in progress and has been since at least January.