Why isn't there Linux style root on Android? topic

This is something I have been wondering for a while and after searching the forums and Google I have not been able to find a clear answer. As a long time Linux user the idea of running your system as root all the time is appalling. It is a huge security risk. But for some reason that is really the only way to gain root access on an Android device (as far as i am aware). Apps like SuperSU allow you to pick the apps that are allowed to run as root, but there is no password or verification that the entity approving the access actually has the authority to do so. I hear all the time that rooting your phone is a trade-off between customizability and security, but every Linux system has a root user and it is incredibly secure when properly administered. What is the reason for the difference?

From what I have read, it sounds like part of the issue has to do with Android handling users differently. I would love to be able to maintain a more limited root function on my devices. Thanks.