Excuse me...
When the wheel was invented, did you say, "It's just a square missing its corners. When ice cubes were invented did you think, "It's just water that got too cold". When Ewoks were invented, did you declare, " It's just dwarves in furry outfits, created for the sole purpose of toy sales".
The "phenomenon" is because the Snuggie is the first great invention of the 21st century. It happens to be a giant leap forward for all mankind. Do you even remember a world before Snuggies? I do. I remember having to keep my blanket drawn below my armpit region if I wished to read a book in bed. And I couldn't see the print very well, as I didn't have my complimentary book light before Snuggies came into being. I remember days long ago when I would wake up in the morning and find my blankets were on the other side of the bed, or worse, had fallen to the floor. That is no longer an issue with the Snuggie. In the past, I would have to coordinate a new outfit each morning. Now, I simply drape my Snugggie over my naked body and head off to work. The combination of the warmth that I get from the front and the open breeziness of my naked backside is absolutely delightful on Spring days.
So, it is not just a backwards bath robe. It is the culmination of thousands of years of human development and ingenuity.