There is a lot of regulatory stuff, particularly around benefits, that push people towards nominally 40hr salaried contracts even if they don't need all 40 of those.
"Salaried" vs hourly is increasingly a scam anyway, but all that benefits stuff is something that would have to evolve. And it could, if people find the political will.
What regulations prevent an employer to give benefits to employees before 40 hours? And how do some employers give benefits before 40 hours despite them?