This is in Bávaro where most of the coast has beachfront resorts, not residential homes or apartment blocks. The places that has the most coastline for residential purposes are Puntacana (well, there it's for the most part country clubs with homes) and Cap Cana. In those places there is still beachfront undeveloped land, especially in Cap Cana.
Macao is another area with much beachfront available, almost all undeveloped. That place has a higher height restriction, so expect residential highrises to pop up in the next few years. As seen in Juan Dolio, a highrise basically multiplies the amount of residential units with a sea view and on beachfront property, certainly more than a single family home or an apartment complex with no more than 4 floors (or a few more, but by law elevators must be installed in buildings with 5 floors or more.)
Plenty of coastline available, IMO. Just not in Bávaro. It goes without saying that anyone living in gated communities in Bávaro, almost all are not on the beachfront.
Úvero Alto is another area with much undeveloped beachfront land, but aside from really being out there, the beach itself while still beautiful is not like seen further south on the coast and even the sand is somewhat different. The water is also rougher with stronger waves reaching the coast.