Why don't Asuka and Mari wear headsets? Shinji, Rei and other pilots wear these headsets:



But why don't Asuka and Mari wear those headsets?
They wear them in a different place, and both of them also "accessorize" them:

Asuka wears red ones that double as hair clips:



And Mari wears white ones as part of her hair band:



Both of them are seen pretty much wearing them all the time.

Also, the Interface Headset wiki page says:


  The headsets used by Asuka Langley Soryu, and by Asuka Shikinami Langley for her Eva-03 test, are both more similar to hair clips in form than the default model. Mari Makinami Illustrious also wears a unique model incorporated into a hairband. For both Asuka and Mari, the headset lies against different parts of the brain than the standard model, but whether this has any functional implications isn't known.