A tasting menu priced per course invites the wrong kind of arithmetic — which plate was ‘worth’ more, whether the soup justifies its slot next to the duck. We price the whole nine-course sequence once and let the kitchen build a sequence, not a stack of individually justified items.
It also means a course can be genuinely inexpensive to make — the mushroom soup costs a fraction of the scallop course — without that showing up anywhere on the page. The sequencing is the product, not any single plate.