Why the Y?

I'm asking out of genuine curiosity about the American custom of replacing so many letters in a baby's name with Y. English is my second language and I'm not from the US, so this is a purely "foreign eyes/ears" experience, and perhaps a synesthetic one.

The letter Y has so much rough edge to it, so much kiki and zero bouba, that I wonder why so many people would associate Ys with cute, round babies. I've come across an explanation that it looks exotic - but the exoticity seems hardly pleasant, it's more like adding the umlauts in the name Mötörhead. All the other vowels sound and look way milder. Then again I might be wrong in my view, so feel free to criticise!