. I am interested in how folks got started and if there is a particular reason why you started wearing them as an adult.
i don't think this has a simple or generic answer (not that you are looking for either).
i've been approached by a few guys who wanted to diaper me. And that's a crucial element for me, most of my kinks grow out of my submissive nature. i cannot imagine diapering myself. i can imagine the feelings of embarrassment, humiliation, loss of control/power, but only in association with someone else getting me to wear diapers. And i qualify, "getting me to wear." i know a lot of people in a D/s dynamic connect through force, being made to do something. For me the Guy who exercises the most control with me is the one who finds my 'buttons' and knows how to push them.
Here's a scenario i can imagine. A Man i really like comes home one day with a bag and says with a big smile on His face: "I got something special for you." Immediately He has latched onto me on several emotional levels. First, HIs smile. i love when a Man is happy, especially in relation to me. Secondly, He's been thinking of me and got something "special" in connection to His thinking of me. When He takes the diapers out of the bag, i might gulp, i'd be embarrassed, but also sexually aroused by His smile and His power to embarrass me by discovering/exposing that i am sexually aroused by His pleasure over embarrassing me. idk, i still don't have the whole affectionate humiliation/embarrassment thing figured out, but it is a powerful collar with me.
If He took one out of the bag and said: "I can't wait to see you in them," He'd be attaching a leash to that psychological collar He found, and tugging it. He isn't really asking, but He is not forcing either, He is just showing His pleasure at wanting to see me in the "special" diaper that He got with me in mind. I'd be drawn further, especially if He went to put it on me, and without missing a beat, started to undo and remove my pants and underwear as though it were the most natural thing in the world. And, at that point, it would be because i would be aroused and He'd see that.
Once He had me in it, He could go all sorts of places with it... He'd have collared and leashed me by discovering an inner place to attach it and He'd know He had latched on to my desire/need to please and my sexual arousal at the thought of doing so, despite my embarrassment and humiliation, which would also mysteriously add to me arousal.
i'd never just start wearing a diaper though, it would be an act of aroused, humiliated, submission for me.