I think the main reason and the main driving force behind this fetish is the creation of the childhood concept as we know today, in the beginning of the 20th century, but especially after WWII.
Not coincidentally, the first reports about ageplayers and people into ABDL are from like in the 1960s, baby boomers essentially. Basically, I think this fetish is deeply influenced by the way childhood is and the society view childhood, as well as the standards of living in a given country.
Like, it is hard to imagine someone having this fetish for being a baby/child in the early 1700 or so, when children were more seemed as "tiny adults working in the coal mines" rather than children. It might have happen, but it would be pretty weird in my option. I think society influences a lot of our kinks. Technologically, as you put it, through the innovation of diaper technology and so on, as well as socially.