I think the main issue is that they released Dynamis as a new datacenter while releasing datacenter travel roughly around the same time. It didn't have a single chance to grow all throughout Endwalker due to the open travel. Nowadays they sort of have a restriction to help it grow, but honestly; Endwalker just taught a bunch of players that its okay to do different activities on different datacenters; which sadly is a slow death for a lot of unpopulated servers. The amount of complaining that the worlds aren't opening up is a good indication of that. I think SE had good intentions when they implemented DC travel, but the playerbase ruined it.