The general differences between men and women (always exceptions to the rule) are interesting to me.
The topic and behavior differences between men and women has to do in part with how men and women typically interpret and respond to intimacy. Your topic and your comment I've quoted is timely in relation to information I've been learning about on the subject recently.
What caught my attention in your comment is the fact that in general the level of engagement (ie distant or actively engaged), feeling of closeness (ie distance vs. closeness), etc that men feel toward their female partner is tied to physical intimacy or lack thereof. Most recently I've learned from watching Youtube videos put out by licensed therapists, psychologists, etc that an extended (or permanent) lack of physical intimacy in a romantic relationship is subconsciously confusing to a man to the degree that it's common for a man to start to view his previously romantic partner as a platonic roommate and starts to act accordingly; the altered view/feeling is completely unintentional on the man's part. In short, many (most?) men apparently stop thinking of their mate as a romantic partner if/when romance ends in the relationship. As a man myself, this reality seems so logical that any surprise about the reality of it is a bit amusing to me.
As such this is at least one reason men can become distant in relationships that have a significant change in regards to physical intimacy. It's a fact that people act differently toward their romantic partner than they do a friend, roommate, relative, co-worker, etc.
Perhaps a concise way to put it would be that it seems to be "in the wiring" that generally a man ends up thinking of his mate more as a friend than a lover if there's no longer any physical intimacy in the relationship. This change could be the "distance" you refer to in such cases.
Or to put it even more succinctly, musician Aldous Harding is correct in her song: Passion Babe, when she sings: "Passion must play or passion won't stay".