Assuming it's separate, why isn't a dessert menu presented to the diners the same time the regular menu is?
Even the wine menu usually, if not always, is.
If there is something on the dessert menu that I want, then I want to know about it before I order the rest of my meal.
Because if there is a particular dessert that catches my eye -- say, a really decadent cheesecake or custard -- then I might either opt to skip on an appetizer or order a lighter or different entree course.
In other words, I want the full panoply of information before I make my selections for the meal, which should of course include dessert.
And just because I may not want to order dessert, doesn't mean I shouldn't at least be informed of my options before I order my savory courses.
Even wine selections certainly are not so relegated to such 2nd Class Citizen status -- the wine list is usually presented or offered to the table with the menu. If the diners are not going to be ordering wine, then the list is retrieved.
Why can't the same dynamics work for the dessert menu?
Why make us wait, after we've ate our meal, to make the dessert decision?