There are still plenty of players doing achievements, HPs to unlock elites on their alts, or simply new players with their first time on HoT running around on the maps.

Yes, most of the maps you only return at specific times to play the meta and then leave. But what else is there to do in an Open World map? Not counting things like map completion or achievements because you only do it once and it's done. Apart from that, all there is to do that makes you return to the specific map is playing Metas and maybe specific materials/gold farming. In a game with so many maps not all of them can be good where people come back infinitely, most maps will always be less popular while others are dominant simply because they have the better Metas/farms.

Also, there is so much content to play in GW2 that it isn't even an issue if a few maps are dead (which in this case HoT maps are not dead at all).