I don't think looks come into it at all, not when you consider the spectrum of clients WGs have sex with!
I think that if your breath is not capable of wilting her houseplants and you aren't literally drowning her in manky saliva
it's probably going to be the intimacy aspect. I was shocked when I found put prossies kiss these days, partly as I knew it didn't used to be the case, but mostly because it was a bigger leap to imagine kissing someone with no affection involved to imagine fucking them..
I think a lot of ladies view kissing differently to men. More romantic/emotional. I've noticed with partners, for them kissing is a gateway to sex and they would always try it on after a big kissing sesh where as for me, it was more about affection and love.
Having said that, a hot kissing sesh does turn me on a lot, it can be incredibly sexy and one of my favourite aspects of sexual contact too - it just took a while to make the leap in my mind from "kissing=emotional attachment" to "kissing=just another part of sex". Without my swinging experience helping me to make that leap I think I would struggle to kiss strangers, tbh, which would be a bit of a shame!!