I've been thinking what makes me attached to diapers - Few things I've come up with
Warmth and affection - I was a bedwetter until I was 7, and can remember the interaction between Mum and I every night as I was pinned into my cloth nappies. Soon after I stopped wetting, my Mum remarried, so I lost a lot of that night time interaction. I will admit that I am a very tactile person - touchy, cuddly etc, so diapers remind me of that time.
Ordering, delivery and drugs - Adrenaline (when you are in the store looking for your diapers, the thrill of the what will happen when you pickup) turns to Dopamine (reward) when you successfully purchase your new wear, so your body makes a highly addictive drug that works directly on your pleasure centres in the brain. Risk = Reward. Buying diapers is a case of low hanging fruit, so little risk, for a lot of reward (or stealing, especially from family members)
For quite a few of us, our first orgasm was in a diaper (I know mine was) - The neural impulses that fire when this happens helps to imprint behaviour and rewards.
Can I pinpoint a time in my life when I decided that diapers were the life for me? No. But, I suspect that these reasons might be part of why I want them.