The girl in Birthright was half Klingon, half Romulan.
Ziyal was half Cardassian, half Bajoran. And so was that baby in Covenant.
I can't think of any other characters who are two alien races without one of those races being human. We have K'elyhr, Troi, Naomi Wildman, Spock.
Why no half Romulan half Betazoid? Half Ferengi half Klingon? Half Vulcan half Pakled? Why do all the aliens always want to get with us and never with each other?
And why is it in pretty much every science fiction show, monstrous looking aliens find human looking women attractive? Jabba should have found Leia repulsive, and he should be lusting after slug women.
Well, for starters, there haven't been THAT many hybrids. (You also forgot Seska's half-Kazon baby). I would surmise that since most of the major characters on the shows (and even a good number of minor ones) have been human, that lends itself to most on-screen hybrids being partially human.
In one of the "Parallels" universes, Worf and Troi have kids, which would be half-Klingon, one-quarter Betazoid, and one-quarter Human.
Apparently, Saavik was initially meant to be half-Romulan (though whether that counts as two separate species is debatable). Apparently they were considering an idea of revealing T'Pol's father in Enterprise's fifth season to be Romulan as well.