I don't think it's a question of willpower. The contiguous US is 48 states, each with the autonomy to calculate and set max axle weight / distance rules and many do. Sliding tandem axles under a 53-foot trailer are not something you just re-architect overnight.

The span under the trailer behind the rear drive axle(s) and the forward trailer axle is much longer than you find on European trucks. That means you need a much longer underride guard. You also have to convince trucking company execs that all that extra weight is a good thing even though they know it's cheaper to pay the occasional settlement after a gruesome accident.

Also, putting the trailer axles further forward to shorten the gap is not possible until Indiana changes their minimum axle length regulation (40 feet trailer kingpin to rear axle centerline) because I believe that while they are the only state to have such a rule, you can't do much interstate commerce with a fleet of trucks and avoid travelling through that state with its central location.

Trucking in the US is massively regulated and bureaucratic and you are going to need a lot more than will to get it to change. I'd love to see safer trucks too but I am not optimistic about seeing underride guards in the US anytime soon.