eHarmony began as a Christian-oriented dating service. As they see it, their mission is to match people who desire conventional, traditional, center-right marriages with each other. Since they began they've branched out a bit and some of their borders have blurred a mite. (Even, as a result of a recent New Jersey court ruling, creating what I understand is a separate gay-oriented matchmaking service, at least for that state.)
Nevertheless, they do not want to deal with people who are on any of the more distant sides of the curves they consider important: gender self-identity, sexual orientation, relationship orientation, etc. They want solid, middle-of-their-road people so that their idea of a "proper" marriage will be encouraged.
Through online acquaintanceships, I do "know" of a number of people who were rejected by eHarmony, most of them (so far as anyone could tell) on the basis of relationship orientation, some of them on the basis of sexual orientation, and some on the basis of gender self-identity.
In particular, and up to that recent court ruling which went against them, eHarmony wants thoroughly monogamous, thoroughly straight people, and if a given person is not, they do not want that person in their system.