You get to deal with harnesses at 4 feet because the regulators simply don't trust private industry when they say, "that's stupid." Even though, as you point out, that's stupid!
tl;dr that's partially due to regulator paranoia, but also because private industry is the boy who cried wolf.
Federal agencies tend to look at requests of interested parties to lighten up on regulation with extreme suspicion. They view companies as indifferent to negative externalities, no matter how horrible they might be. Just look at the chemical composition of wastewater from fracking. Haha of course you can't do that because although it's a virtual certainty that stuff in that wastewater is harmful to humans, they're not required to tell anyone what it is, and it's not in their best interests to do so. We'll find out in 20 years when the cancer clusters crop up.
To compound that problem, humans have an optimism bias that means that without domineering government interference, they simply won't prepare adequately for disasters. Look at the BP oil spill. How much thought had BP put into how to seal a broken deep sea cap? About 2 pages' worth (the literal size of their contingency plan) because EPA didn't force them to do more. They had to jury rig equipment on the spot to quell the flow, and there was a very high chance that their solution could have blown out the whole well. You might be wondering why they didn't spend more to prep since the oil spill quite predictably cost them a lot of money. It's because they were stupidly optimistic and didn't consider a blowout to be much of a concern, even though the circumstances leading to it were easily predicted.
