The problems with this are multi-layered, and that historically has been the largest part of the problem.
1. Most people are impatient creatures and if something does not work in a short period of time they go on to something else and then emphatically state that "nothing works".
Any form of PE and this runs the entire smorgasbord of available methods is going to take a great deal of time, patience and most of all diligence. You have to stick with any single method 1 - 2 years before you even begin to make any kind of value judgment for that particular method.
The greatest percentage of men can with enough effort and time investment over a long period of time achieve some enlargement.
2. The most difficult to achieve are gains in length:
The reason for this is the structure of the penis and the natural variations of that structure between individuals. There are two main ligament structures and a combined structure composed of a web of ligament structures.
The tissues of the penis with these exceptions actually stretch relatively easily in length and in diameter or girth.
Some men have ligament structures that will stretch and respond well to the various stretching techniques and the ligament structures in a small few could substitute for the cables supporting the Golden Gate bridge. In these men these structures simply will not stretch.
That small percentage will not respond and this is very real. Some stretch easily and permanently, others tend to want to retract after stretching losing the gains, and a few don't want to stretch at all.
This fact is what gave birth to the various surgical enlargement techniques.
There were good procedures in the earlier days of PE Surgery, the sad part is that many were not willing to compromise one thing to gain something else. The compromise with a good job of ligament modifications is erection angle. If one is willing to compromise erection angle some of the techniques done in the 1990's for length gains were quite effective.
Girth enhancement as has been said by another poster is almost too easy to achieve. My best results when I was in to this was achieved with vacuum pumping and after a couple of years at it the gains were permanent. I have heard of other methods that are supposedly equally effective, but, vacuum pumping worked best for me so I can only speak on personal experience.
3. Time Time Time Time Time
There are people who may do better, but, to see any significant length increase most individuals are going to be at it a minimum of 3-5 years. The first 1.5 years of that will show very little in gain and it will over time begin to accelerate to a point. Gains will happen and then plateau and happen again and plateau.
When it comes to girth I started seeing a very obvious difference by the end of the first year.
At this point I am thick enough that my other half has trouble in a deep throat act so I am going to leave things were they are.
4. What are you willing to risk?
The guys who are probably going to crack this nut the most effectively are those involved with chem PE. There are some guys doing pretty well with this right now, but before one even thinks of beginning it, one needs about 2.5 years of study in anatomy medicine and pharmacology.
These guys are putting it on the line and risking everything, but watching this front appears to be one of the best ones and more interesting ones, and most likely to achieve success.
Hope that this information helps