Generally in MMOs, the majority of players tend to pick DPS jobs. Some players like to see huge damage numbers, others are less inclined to take the lead by tanking or having the responsibilities healers/tanks have.

I’m sure there’s data somewhere but it’s probably something like 3-4 DPS mains for every one healer/tank main. There’s really no way to mitigate this, people play what they enjoy most which is DPS for the vast majority. It can improve some with the addition of new tanking and healing classes, but DPS queues will eventually go back to being the longest.