Cool question, and i too have seen a lot of guys who want sex with guys who are not into kissing them. i'd stop shy of putting the question in universal terms though. There are guys who wanna kiss guys too.
i think for some, it may have to do with the 'spectrum.' While we use black or white terms for communication, reality is we are all individuals. I.e there is infinite variation on who and how we want/need/experience intimate desire/connection/pleasure, etc..
One thing i experience personally when it comes to kissing is it involves different need/emotion/desire than sex does. Kissing can overlap and definitely enhance sexual connection for me, but it also has separate and unique factors (that word sounds way too clinical to me). i don't completely understand all my needs and desires, and suspect that is true about a lot of emotion for most people? The desire to kiss or not is more of an emotional thing, so it's harder to wrap in words?
For me, there is a decided visual component. i have to be visually attracted to a guy i am kissing. The same is not true about sex. For example, for me, a Guys desire/need to penetrate, fuck and inseminate me with Himself are all driving factors that evoke and connect to my reciprocal desires/needs to be penetrated, fucked and bred. With sex, i can have a one and done hook up... a Guy i want to kiss? I'd want Him again, something ongoing? Which is not to say that cannot happen with sex. Maybe it's a romantic component that i (emotionally?) associate more with kissing than with sex? We can fuck and be friends, can fuck and be done, but if we kiss, you're gonna have to propose? lol
Also, it's not just lip kissing. i have an ongoing FB who i 'love' and i think He 'loves' me in a way. But i doubt either of us could imagine having a traditional romantic relationship, even though He has bred me 2-4x a week for going on 6 years now. We have never lip kissed, and i suspect neither of us has the inclination to. But, i kiss all over His body. The tip of His cock, His anus... and every other part. Tender, affectionate kisses. And, He kisses me... but only when i a face down, prone underneath Him. my back, sides, shoulders, both passionately, and also gently affectionately... both drive me wild. He doesn't kiss my ass or penis though.
my FB is a good example of (absent) visual attraction. He's hairy, has facial hair (which never find attractive). He's a body builder, which has never been a particular attractant for me, but i've really come to enjoy His defined muscles and touch, kiss and lick them. my kisses on His body are definitely affectionate, but i don't feel or even imagine those feelings about kissing Him on the lips or being kissed on the lips by Him.
A lot of mystery to kissing for me.