i guess strongest point is...
sexual pleasure
diapers are the first thing a baby is more or less stimulated by it's diapers
24/7 in contact with private parts and thus giving more or less constant feelings of all what that diaper brand is letting you feel there
most babys are enjoying wet and messy diapers because
the wet feeling is warm and comfy on the skin down there
also the wetness feelings turns a baby on - from sexual pleasure
babys also feel sexual pleasure - just like babys do
most children have their own ways of looking for sexual stimulation - that is true and normality
this is independent from beeing sexual mature
it is known that intense sexual stimulation happenings in childhood lead to sexual imprinting what may define sexual fetish and desires in adulthood
https://en.wikipedia.org/wiki/Imprinting_(psychology)#Sexual_imprinting
in other words:
the diaper was the first thing gaving you a intense sexual baaang feeling - and you wanted that feeling again and looked for it like everyone would do