Why? Because remembering to not do things is a restraint that is extremely mentally burdensome and thus difficult to get correct 100% of the time.
When you're the CEO of a publicly traded company, getting paid millions in stock comp to run that company, you don't get to use the excuse "it's mentally burdensome". The whole reason they're in that position, getting paid those obscene amounts, is that they're supposed to be able to handle the burden. If they're not able to handle it, they should step aside for someone who can.