Welcome to the Weekly Question Post on c/guildwars2!
This post is dedicated to those questions that you might not think is worth making a whole post about, but sure is worth getting an answer to ;)
Remember to also take a look at the links in the sidebar, which holds lots of great resources and information.
There are times where maps are not that full, because not many players are playing, which is perfectly normal. Your server has nothing to do with it, because GW2 uses mega servers, where all players from a region are basically on the same map instances. Your server is only relevant for wvw right now.
The game dynamically adds instances of a map, when more players join a map, to keep them at a better performance level. When players leave, instances close again. This is best visible when metas happen
You can have bad luck and get put in the “last” instance with the few remaining players, but that shouldn’t happen that often. If you see are on a meta with few players check the lfg for maps with commanders, they are usually full of players.
The commanders/mentors you see are probably players temporarily activating their tag for a single rift/event and are not doing a longer rift hunt squad.
Feels similar to the launch of the last expansion, where they would finetune new map instance creation over the first weeks.