Mudra why so many ninja don't use them?

[Burmecia]

Sub-optimal would be just using them on cooldown or using them on the wrong abilities. (like single target Doton, which often stems from the wrong assumption that DoT effects tick every second, most likely learned in other mmos.)

Not using them at all is just ignoring a main feature of your job and expecting other people to carry you because you can't be bothered.

Motives for bad play can be just are varied. Ignorance, laziness, some other nebulous reason.
If someone wants to make spectrum out of bad gameplay, then I say go for it.
But for now, for whatever reason mudras arent used, I'm going to call not using mudras sub-optimal gameplay.
Because surely it it below optimal to not use mudras.