Because the difference between an M2 MBA and and an M1 MBP isn’t nearly as big for most people as upgrading from a 1080p display to a 4K touch display on your typical PC laptop.(which are typically the two options given on PCs)It's not the same thing
Most PC vendors, for instance, allow you to upgrade just the screen tech on a variety of laptop models.
It's a really nice way to get a machine that very closely matches what the customer wants
Apple offered upgraded screens on the first unibody 15” MBPs because back then the only way to get more usable screen real estate was to increase the resolution. Every MacBook in 2023 has a nice, high quality Retina display that can be scaled with a variety of resolutions.
Surfsalot can laugh all he wants, but for most people who feel they need to pay for a slightly fancier Retina display, they are going to buy the MBP regardless because probably need the pro for other features besides just the screen.