Heavensward Leveling... aka Northern Thanalan Leveling

[Kaedan]

Sure there's more players but am i missing something else?

Yeah, missing it even though you said it yourself. Two reasons:

1) ARR FATEs are MUCH easier to complete than HW FATEs.
2) More people, faster the FATEs get done = more XP.

That said, dungeon spam is far better. Yet the queue can get long for DPS, so FATEing is a good filler.