It would add another year to the production of the tree you are buying. Grafting is easy enough that most people can graft a pollinator branch onto their own tree if they are so inclined.

" I wonder why the industry doesn't simply graft a few branches of one species onto the stock of another in the first place?"

They do. Multi-graft (or sometimes referred to as multi-budded) trees are rather common in the fruit tree industry. I am not talking abut the "fruit salad" trees offering various kinds of different, unrelated fruit types but common fruits like apples, pears, plums and cherries that require a second, different variety for successful cross pollination. Sometimes referred to as 3-in-1 or 4-in-1 depending on the number of different types grafted, these are intended for home gardeners that do not have the space for multiple separate trees and do not have the time or inclination to do home grafting themselves.

Multi-graft fruit trees.