Or why would a successful young actor and singer like Jim Nabors choose an old man like Rock Hudson? That is, if you believe the story from well over 40 years ago that Rock Hudson was going to marry Gomer Pyle and his new name would be "Rock Pyle".
Why would a successful actor like Tom Arnold choose to marry a fat ugly repulsive woman like Roseanne Barr, when he could have sex with just about any Playmate that he wants?
If it was me back in the early 70s, and I was at a dinner party, given the choice of sitting at a table with Roseanne or Jim Nabors, I would have sat down with Gomer. I wouldn't have been able to eat, if I had to look at Roseanne across from me because it would have turned my stomach.
So why would Roy be attracted to Gomer?
His father, an auto mechanic, abandoned him as a child and he remembered his stepfather Wally as a marine. Roy was beaten on a regular basis by Wally and was usually "covered with bruises". His mother divorced Wally after Roy got two black eyes, but later remarried him. During WWII, Roy joined the Navy. Maybe that's where it began.
Gomer Pyle worked at Wally's Filling Station in Mayberry and later joined the marines. Maybe that was the attraction. ;-)
The more important question, is why would any man, choose another man's filthy ass over a woman? Do his looks even matter, when he's looking at his backside?