It's different for different people. Personally, I wasn't abused, wasn't abandoned, had wonderful loving parents that were present and raised me well. For me it certainly doesn't come from a negative space although it certainly does for others.
That said, the why isn't really important to me. I'm happy, confident, married to a wonderful women that accepts and participates in my diaper play and I accept my desires and have no desire to change them.
Over time you'll find the why matters less than just being happy and comfortable with who you are.
Snugglebear