Who the hell made ukes dick size small as a stereotype in BLs

Everytime I read yaoi, the dude's dick is so fucking small... No hate to guys with like small dicks out there but still why is the seme always 8 inches and the uke is like 2 inches?? The average Asian guy has 5 inches! (hard) American has 6 (yes they're bigger according to some studies) it puts me off seeing the size difference everytime... Its even worse when it's uncensored and they have no pubes.