Well for me is the sense of accomplishment
Leveling crafting classes its not just a mindless grind or press one button and let the bar fill up, it actually takes a bit of thought on how to craft the actual item especially if you want it to reach high quality, with the different tools and skills that you get.

Also with the thing of being able to have all classes avaliable to you and the ability to mix their skills up also opens up to new techniques on how to craft, fight and gather.

Ive felt a bit of an accomplishment whenever I beat the hard modes for the primals (big ass summon bosses), same for when I maxed my first crafting class, etc. Unlike WoW even though WoW is a bit more polished on the raid side, the game just feels a bit dullish when it comes to achievemens and class leveling, I assume because of after 10 years the game has been gradually making it easier so it doesnt matter as much as it used to and its barely focused on "Lets get to max level and clear the end game"