Because people will shoot themselves in the foot if you give them a shotgun. A big part of why the Mac as a platform blossomed in the late 2000s forward was because it was much less likely you'd get hacked by clicking the wrong link or just opening an email than it was on a Windows machine (among other reasons)

And, all of that said, Apple hasn't said anything about not letting people have full access to their disks. Just that you're going to have to be very intentional, click through a very scary warning, to do so. Happy to do that to prevent my mom or dad from accidentally opening up their machine to every hacker in Belarus or worse yet Facebook