The 'why' in porn aside as it's been reasonably answered multiple times in this thread....
Re: Cleanliness of cut vs. uncut. Clean is clean. However, whether women get yeast infections (for example) it isn't a simple matter of showering. There are a variety or harmless reasons a woman can get a yeast infection that have nothing to do with her per se hygienic habits. Uncut men are subject to the same circumstances.
Also, our skin is one of the ways disease, bacteria and infection enter the body. Because the skin of the head grows many many many many times thicker of the cut man than the uncut man...uncut men are more susceptible to disease and infection because the skin under their foreskin and on their dick head is the thinnest on the body next to the insides of the eyelids.
That's science fact.