Why did so many '80s band names consist of the same word twice?

kinda surprised there wasn't an art-damaged 80s band named Foot Foot

Well, it can act as an intensifier in other languages too - "very very good" is better than "very good" and "sehr sehr gut" is the same.

I'm not convinced about the childish thing, unless it's done with specifically childlike words - in fact, usually I'd say that more childlike would be similar and rhyming words (can't think of band names other than Oingo Boingo, but stuff like that and 'Mellow Yellow' etc). Repetition in band names does tend to be poeticism without meaning, though, which, to be honest, is pretty much what lyrics are.

xpost

Would totally be in a band called Foot Foot.

dada doesn't refer to the word/sound children tend to use...

xpost

Yeah, but it evokes that same primal/childish or child-like association. As for the "real" origin of "dada," there are contradictory accounts of how the word was adopted (surprise, surprise), but the Dadaists seemed to relish the potentially childish meanings (e.g., rocking horse).

Well, it can act as an intensifier in other languages too - "very very good" is better than "very good"

Good point.