Interesting idea, and something to mull over of course.
I tend to get long winded and could write ad nauseum for infinity on the subject, especially when taking under consideration how porn evolved from risque erotica to what we see "today" (i.e. mainstream porn post 90s-gonzo).
Suffice it to say that there are many male perspectives on the subject. For example I have read time and again that, in mainstream porn, if the scene "ends" with the guy "having" to jack himself off to completion, then that was a sign of "non-hetero" activity... Meaning that those who believed in such a statement would suggest that if any "hetero" man should end the porn scene with either the lady stroking him off to the cumshot, or blowing him until he cums, with the man "never" touching" his own dick.
There are numerous other perspectives which could be expanded and liberally discussed about the matter. In the 70s, the "facial" cumshot was not as rare as some would think, but would indeed be principally instigated by the female performer, who would just happen to end the scene by finishing the guy off herself on, or near her face.
The "modern" facial cumshot where the dude jacks himself off on the lady's face started in the 80s but was still a rare occurance in the sence that no self-respecting lady would actively ask for such an act to be performed, and like anal or DP of the time, was a rather "niche" act which was reserved mostly for the "dirtier" performers, for the films which would focus on such activities, such as anal-themed flicks or such. Personnal note: a late 80s film with Raquel Darrian called "Welcum To My Face" which basically barely has mug-shots, so absolute rip-off. But then again, this was the 80s!
In the 90s thanks to Buttman (and slightly later, John Leslie's The Voyeur series) and especially "Rex Borski" and those early Rosebud pictures, gonzo was born and the whole idea of finishing off on a girl's face became more common, and soon enough it was almost "required". If the in the 80s girls who refused anal would be out of the business by the time the 90s rolled in, similarly in the 90s if girls didn't take it in the face, they would soon become extinct. By the mid-late 90s, the trends were shifting, and we saw an exponential increase of depravity, from Inari Vachs' earliest super sloppy drooling blowjobs (which were unheard of, for the most part at the time) to the almost required anal in every scene gonzo video around.
By the time the Y2K hit us, we were already split by the Vivid shot on film condom-clad cum on a butt or belly story-oriented film, to the POV handheld camera strictly focusing on anal, DP, and facial cumshots.
In retrospect, perhaps the idea of a male manually finishing himself off at the end of a scene could be an extention of what the smut producers felt was a necessity in order for the porn consumers to feel, in a way, "connected" to what they were watching on the screen, or maybe it was just the natural "evolution" of what porn had become through the ages.
Needless to say that whatever the intentions may or may not be (as of course everything is purely subjective and open to one's personal interpretations), in the post Y2K, porn has become a veritable industry which caters to almost everyone's niche tastes. Meaning that if a guy does NOT want to see a porn where the guy finishes himself off, well there was always the "About Face" series where the girls would finish the guys off, 99.9% of the time to dismal and forgettable cumshots, to the blowbang scenes where towards the end the guys would be jacking off around a girl (busy blowing 2-3-4 guys and such) and just dropping loads whenever it happened.
Cheers!
