I don't necesarrily think cock size dictates whether you can or should be a cuck, i'm sure there are plenty of well hung, alpha male CEO's, soldiers, oil rig workers, prisoners etc. being cuckolded without their knowledge, but I do think smaller cocked men do gravitate more to being cuckolded, as it gives them a tribe to belong to (having a very small cock, or never getting women for sex is quite lonely and isolating) BUT the one thing my wife and I believe is, its very hard for a small dicked man to be dominant in the bedroom, it just a dynamic that doesn't work. I have tried on occasions and literally openly laughed at while I tried to fuck them hard, and told to stop wasting my time trying to be someone i'm not.
So I think submissive men also find themselves as cuckolds, whether by choice or not. I don't think its always about size, but smaller dicked men probably get cheated on more often, so that opens the door for them to desire being cucks to bring the cheating to and end.