At a guess, Dancers don't have as much time to experience their skill set - most healers and tanks tend to have run through every single instance in-game to get to the level of competency that is required at level 80.

Perhaps you are simply unlucky in the draw, or the tank is pulling mobs too far away from the dancer, or knockbacks and other mechanics are preventing them from approaching the mobs. It is understandable that DPS doesn't want to waste 2 GCDs to work through Standard Step in such cases, doing exactly 0 DPS because they're more than 15 yalms away from any mobs. It is hard to know if the additional 5% damage buff is going to compensate that 0 DPS. For raids under level 70, Technical Step doesn't exist. For 70/80 raids, it is still 3 GCDs that can be wasted, every 2 minutes, although I expect it is less that than just inexperience with how Esprit works for Technical Step, and whether or not a 5% damage bonus is worth those 3 GCDs if the end result is 0 personal DPS during the Step.

Dancers may not be aware that increasing the Esprit guage allows Sabre Dance to be used more often, and this may be worth using Steps to increase that guage. However, Esprit is tricky, in that the tooltips imply it is auto-generated by weapon attacks/spells, when it is only a chance to do so. If a Dancer tried it out and it is perceived that it doesn't really do much, it may be ignored.

If one is trying to maximize DPS, one really requires a dance partner when testing things with a level 80 target dummy.

With a single expansion to learn your job, there are bound to be people who haven't realized their full potential yet. If you are in story-mode raids, you should expect more players to fall into that category than not.