It'll allow states to race to the bottom in worker safety, which I suppose is the idea.
It might also make compliance overall more expensive by creating a fragmented patchwork of regulations and practices, which increases complexity. Look at the effect of different states having different fuel formulation requirements on the oil refining industry.
A lot of the cost of regulatory compliance comes from complexity, fragmentation, and cognitive load. Simple uniform regulations are cheaper and easier.
Not just that, but one central institution can employ experts and do studies due to the larger budget. 50 small ones are just going to scrape by with the minimum.
Maybe there's a middle ground where states can have local-overrides - if their residents agree.