The EPA has a bunch to do with the lack of choice.
It costs an extortionate amount of money, into tens of millions of dollars, to test the engine and driveline group for regulatory compliance... It has to be re-tested as if it's a completely different engine if you put it in a slightly different chassis or even make a simple change like a different output gear ratio in the rear axle or transaxle differential.
The HooHaah about VW using multiple fuel maps dependent on driving conditions was the regulators flexing their muscles. The powertrain engineers used several different fuel maps to control emissions at a reasonable level under varying driving conditions without completely killing engine performance.
The fact that one of those conditions was closely related to the IM240 test bed exposed the FACT that the IM240 isn't simulating real-world driving conditions. It's very controlled. A fuel map can be developed to meet certain specs under those very controlled conditions.
The real world isn't a closed and controlled system like these ivory tower armchair experts would like to believe or even create... VW and various engineers at VW paid a heavy price for exposing the fact that the Emperor has no clothes.
The quiet murmurs, for now, from the top-down regulator/administrator class, otherwise known as bureaucrats, that "we should be working toward self-driving cars under a central traffic admin" ain't to help us... it's about allowing the bureaucrats building another agency feifdom to exert additional control over how the serfs live. The unfortunate truth is that You and I are the serfs in their eyes.
Working on this kind of tech is fun for many engineers and they don't step back to see the leviathan they are creating under the purposeful direction of the extremely clever and manipulative, but not very bright, bureaucrats.