Its just camera angle
When you take pics of your cock while sitting, it look huge, like your cock go to your nipple...lol
In thoses videos they are not sitting they almost laying down, and it look like theirs cocks go to their faces, that why
Or also some even use distortion on there cams, like if you compare the cock with the hands, the hands look so huge, but the body or the legs look ridiculousy small, this is manly why they never stand up, because it would be harder to cheat
Btw some of thoses guys are also on LPSG (I remember some of them) and they added pics on there profiles, and they in some of them they dont look as big, just angle