I agree with what Necare said, but differ in the fact that i think it is part of human nature to want, at least to some degree, that security and safety we felt when we were a child. The only difference is how we obtain it, some strive for excellence in all they do so that they can drown their insecurities in a sea of accomplishments, others strive for money so as to provide for themselves a sense of security they lost from childhood, while others develop anything from destructive habits such as biting nails and fidgeting in order to deal with their unfulfilled need for comfort and security. Infantalism is the utter incarnation of this basic human desire, satisfied in the most literal sense possible. If you think about it, if you can remember being coddled in your mothers arms, that sense of complete contentment, and security it gave you, you would have to be insane to not want at least some semblance of that in your everyday life, nay, every moment of your life. But, alas, our society tend to deny those primal, basic feelings, which later manifest themselves in strange ways later on in life.
Back on topic now, I believe that as the internet continues to penetrate the everyday life of the average citizen, more and more poeple will begin to "stumble" across hidden desires such as wearing diapers, and as such that increased exposure will lead to more people becoming aware of their preferences. You cannot "make" an AB or a DL, they exist with that seed planted deep within themselves, it is just if, by chance that seed is stirred and begins to grow.