Oh wow... I have many theories on this one.

I believe it has something to do with cerebral spinal fluid and optimal performance of the nervous system. When we relax, our mind enters a different state of being biologically, electrically, and spiritually. Meditation is the rejection of external stimulus leading us into a healing stage.

ASMR embraces external stimulus, and as a result those of us who are more in tune with our senses, are pleasantly surprised with new sensations.

Medicine only recognizes problematic symptoms as illness. ASMR is a positive experience which is healthy, so it eludes scientific scrutiny.

Modern television and media has strictly adhered to the philosophy, that louder, larger and more intense is the most effective way to grab and hold our attention. If you ask me it's the core reason why my television viewing habits are absolutely minimal these days. TV makes people zombies, and ASMR, while it does make one very relaxed, the sensations which go along with the experience, are highly spiritual, rather than the soulless void of television.

My first chakra, lucid dreaming, and third eye experiences were while watching ASMR videos. Binaural beats are another great relaxing method, if you are extremely high strung and stressed out. In fact, it was progressive with me. It took binaural beats to knock me out of a crazy OCD stressful period of my life, and ASMR brought me into deeper relaxing states of being.