On MacOS most of the files that makeup the system are now write protected (not just the file permissions, but something called "System Integrity Protection" or SIP). So you can't overwrite them. You can add a new install, but then you have to know how to change your $PATH to view that location first. That is just one more thing you have to know.
Apple did start to have a binary in the default location that was really a chooser that would respect per-user settings and re-direct you (exec) to the "right" install, but they seemed to have backed off on that.
