Fuel economy regulations are based on vehicle footprint and weight. Small trucks are small and (were, still would be if we still had them) fairly heavy for their size making them bad for compliance. A small vehicle is also going to have harder lines (less physical space for clean curves) so will have worse aerodynamics.

On the other hand, all these arguments completely go away for electric cars, so there would be space for smaller e-trucks.

You think the government won't set energy efficiency requirements for electric vehicles similar to mpg?

They put energy requirements on dishwashers, they're not going to give EVs a pass.

That is interesting. I wonder if that is why Ford got rid of their small pickup (The Ford Ranger) for several years from 2012 until 2020.

It did come back last year, probably after meeting new regulation requirements.

That's exactly it. IIRC they even said so at the time. They were already producing the "new ranger" elsewhere at the time so they could have just imported it but looking at the MSRP difference between it and a based f150 vs the size of the market they decided it wasn't worth it.