The first part of your questions more seems to come from the line that from an intellectual standpoint you dont understand sissies.
On this point let me say that as an AB and a father of a 10 month old son, there are some things that I missed out on when I was a child and that part of the reason that I am "babbyish" is that I am trying to recreate or maybe recapture part of what I missed out on. Most of the mainstream population out there would in fact call this being a sissy. The reason for this is that for them they can't seem to understand why we can't "just get passed it". What they fail to take into account is that everyone has their own way of dealing with things in there life and things that have hapened to them. What will work for me might not work for you and the reverse is also true.
Also like Diaperbayb said for some of us (myself included) it can be a complete or perhaps just a large contrast to our daily life. When we try and balance out our lives some things need to be addressed.
Also I know that you are just generalising when you list the three categories that you did and that was a decent shot at trying to capture the general spectrum of what is out there. As far as why we do the things that we do there is only one piece of advice that I can give you. When you are trying to understand a group of people and why they are labeled the eay that they are, you need to consider two main things:
1. The label that they are being given, is this comming form themselves or is it comming from main stream population?
2. If the label is comming from mainstream population, it is usually a stereotype and does not generally accurately reflect the person in question.