The problem with a fixed loft
A pillow is manufactured to one height and then sold to everyone. That works for whoever happens to match it. For a side sleeper with broad shoulders it sits too low and the head tips down all night. For someone who sleeps face down it props the neck into a curve it was never going to hold. Both wake up sore and both assume they picked the wrong pillow, when what they picked was the wrong number.
What changed
Putting the fill into two removable quilted layers turns one number into three. Nothing about that is complicated, and it is the reason a single pillow can serve a household where nobody sleeps the same way.
Why coiled fibre
Adjustability is worthless if the fill gives up. Solid foam holds a dent once it has been slept on for a season, and down needs shaking out every morning to look like a pillow at all. Coiled fibres behave more like a bed of tiny springs: they take load, let go, and let air through on the way. Lab testing put the support holding past the three year mark, which is roughly double the life people report from a supermarket pillow.
Where it is now
The company runs out of Las Vegas. The range is deliberately short, because a pillow that adjusts removes most of the reasons to sell six of them. This site keeps the US range in one place with the sizing written out plainly, and every order goes through the Amazon listing where the price and delivery date are current.