> "people [...] find it harder to approve of a marriage ending because one or both people felt unfulfilled"

I think that in a really incompatible marriage one feels not only lonely, but not loved as well. It's quite hard to love someone so different from you (*) that s/he seems "alien", odd or unknowable.

Therefore, saying "I want to divorce because I'm not feeling loved, ever" (while not blaming the spouse, just stating your own feelings) might be more acceptable to most.

(*) Some people might say that it's easy to love someone different from you; I'd say that's more likely attraction that love. Opposites often attract, but seldom get along well.