In addition to what eurasiantiger said, it's been a best practice for decades to keep the root environment default and untouched. At a behavioral level, you do

In addition to what eurasiantiger said, it's been a best practice for decades to keep the root environment default and untouched. At a behavioral level, you don't want to make root's environment so comfortable that you use it more than you should. By keeping it vanilla /bin/sh you encourage admins to log off and do their usual work in their usual environment. At a technical level, as soon as you start customizing the root env you open a lot of doors for dynamically linked dependencies to whatever shell+goodies you switch to, which expose root to potential vulnerabilities. You also increase the risk that updates will break root in some obscure way, which will not have been tested by the OS Q/A process.