I think that:
1) Plenty of men hear about penis enlargement and don't believe it's worth the risk of injury even when they're dissatisfied with their penis.
2) Men hear about penis enlargement but don't believe it gives real results (because of the bad rep from pills, etc.).
3) Men only learn of penis enlargement in the form of pills, etc. and not manual exercises like jelqing and never see results from it (but spend quite a lot of money).
4) Guys with ED look for natural means of curing their ED, find jelqing, and end up gaining size along with curing their ED.
5) Then there are guys like us, who are insecure with the size of their penis, have either tried pills or never tried them in the first place, that find communities like this one and take the time (because it does take a lot of time and dedication) to enlarge their penis.
6) Also there are guys like us, but they either go to hard and fast and end up injuring themselves, swear off all PE and never try it again - and also make sure they tell every guy they can not to even try PE because they'll kill their dicks. Or alternatively there are guys who PE, but do it off and on and never stick to a dedicated routine and therefore never see gains.
I find that a lot of guys with small sizes also blatantly disregard the possibility of enlargement simply so they don't get their hopes up. I've noticed this a lot on small penis support groups and things of the sort, also the LPSG area was entirely anti-PE until Big Al smacked people around over there, but there are still plenty of men who completely disregard the possibility of enlargement working or think it's a complete gimmick. I can't really blame them for thinking that though.
Keep in mind a lot of PE'ers are probably obsessive compulsive to a point and have at least a minor case of body dysmorphic disorder too, so guys like us are more likely to search for means of penis enlargement then other, more "normal" men.