I think the Ashtabula crank is a great work of American ingenuity. They were reliable as all get out, manufacturable, and easy to service with just a crescent wrench and screwdriver. I've got two bikes with them.
When I was a kid, there were basically one-piece and cottered cranks. The cottered cranks were a nightmare to service -- getting those pins just right so they were actually tight and didn't start to wiggle after a few miles took some skill that none of us possessed. But the crank on a Raleigh was not a functional improvement over the crank on a Schwinn. I doubt it was materially lighter. When you got a bike with one of those cranks, the upgrade was a "cotterless" crankset, which we now call square taper.
For the one-piece crank, most of us had no reason to upgrade one, but there was no upgrade path if we did want to. Making the whole thing out of aluminum was probably not a practical option. So, experiments with lighter components ended up leaving the one-piece in the dust. Still, when we talk about ways to make the universal low cost practical bike, ditching modern crank sets would be a good place to start.