This is just where they make the babies.
Medline has had a monopoly since the 1950s, when they first brought their signature style into the world. They've produced about 25 million of them since the '80s alone. Once you throw in numerous washings (what, you didn't think your brand new kid was special enough to get a brand new blanket, right?), that explains why almost every baby born in an American hospital, and countless around the world, have been tucked inside their product. The reason this particular item took off? Simple: the low cost compared to their other models of blankies. Thankfully, most babies aren't fussy about design.
And they've perfected a placenta-stain-removing laundry system.