Why cant the smartphone companies just pre root the phones at the factory and save everyone the trouble?
In the world of Linux (and UNIX) ‘root’ is the supreme user level which has the rights to perform any task. It is similar to the Administrator user on a Windows PC. By default, only the Linux kernel and a small number of core utilities run as this superuser. But by ‘rooting’ your device (which means the root user level is available to all apps) then many of the security mechanisms are made null and void. This is because an app with root permission can modify any other part of the Android OS including the operating system itself, the kernel, and other apps.
Therefor, by giving root to the average user right out of the box - it opens the unaware to security threats. Root is for power users only. 90% of people would never see any benefit, and possibly even some hindrance to day to day activities should the device be compromised.