Correct. Most ASMR audio focuses on whispered voices and other quiet phenomena like rustling, tapping, etc. that tend to induce those tingling sensations in the listener.
IMO, anyone who is interested in being spoken to while little (patronizingly, tenderly, gently, etc.) might enjoy crossing ABDL and ASMR. (As might anyone who likes the crinkling noises of diapers or the rustling of plastic pants. As might folks interested in hypnosis.)
As for the why, anyone who experiences ASMR can answer that; the tingling and general wash of euphoric feeling can be very sensual and almost sexual, and thus might be particularly attractive for littles who prefer not to mix sex with ageplay.
It seems like there must be some of this out there--hence my question. For instance, several years ago on an episode of the Big Little Podcast, Penny Barber mentioned that she was interested in producing some ASMR content. I don't know if that ever amounted to anything.
P.S. Here's a link to Binkie Princess's stab at some such content. Might better illustrate what I'm looking for.
https://youtu.be/8RcCND-rDPU?t=1m16s