As Chasing pointed out, coatings are about protection.
But, if you smoke carefully with a new pipe, there is no need for it.
Uncoated chambers also allow you to experience the natural flavors of briar, that typically get masked with a coating.
For an experienced pipe smoker, buying an expensive pipe, a coating makes zero sense. You buy that ultra high end expensive pipe to experience it, in it’s full glory, and with an uncoated chamber, it’s like you make it your own too, forming a carbon layer over time.
P.S. Yeah, those pricey Dunhills have coatings which is odd, and the Danish like coatings too… The Italians don’t like coatings, but you can occasionally see them. Viva La Italy!
LOL
Oh my a Castello with a chamber coating, that would be horrific! LOL