I think regen braking only helps if the load is on the bed. If it's on a trailer, the trailer will have normal breaks and a lot is lost. (Edit: spelling)
Trailers may not have regenerative braking today, but that's a chicken-and-egg problem; trailers already have wiring hookups, and once EVs become the default for personal vehicles, it's easy to imagine that regenerative braking will become standard.
braking
It also doesn't help if you have a long freeway trip where you don't brake.