Kissing, in some ways, is much more intimate. Hell, we only do the act of kissing for that feeling and intimacy knowing full well we ain't cumming from it. Sex on the other hand, is often done just for the satisfaction of our physical needs and that can be true even for women. Women can get wet as much as we get hard but neither means we have an emotional attachment to one another.
Two people cannot mouth kiss unless they are in each other's face so to speak. For many cultures, tongue kissing isn't even really a thing and public displays of affection are discouraged. My Korean gf, though quite westernised, is still embarassed to give a peck on the cheek in public (though she secretly allows me to do other things lol).
In terms of MLs, a HJ or even a BJ can be seen as merely a physical thing which women can detach from any emotional connection. It's just an extra they can charge money for. A WL once told me that it's easy to fuck a guy, she shuts her eyes and get on with it. The same girl said that many others don't DFK as that's reserved for their boyfriends, significant others or husbands.
Thai people even have this thing called the sniff kiss where they don even touch lips but "affectionately nuzzle" each other. Again, it's just how they display affection and just because it's different to the DFK we know in western culture, doesn't mean their version is any less.
Kisses are built on nothing but emotions as they say. Some of us punters love the GFE experience because it's what we are conditioned to expect from a relationship. We trick ourselves that the MLs and WLs are into it as much as we are. We are made to believe they want to kiss us for reasons other than money. But we all know it's not true.
Imagine working in an industry where you give pretty much everything of yourself to customers. Mentally, anyone would want to save a bit of intimacy for their special someone in this life (be it kissing or anal lol).