The vast majority of the linux software is installed in directories such as /usr/bin and /etc where only root has (and should have!) write permission. Users can install (some) applications in the own home directory and run them from there. These applications are not autmatically added to the path of other users, and therefor not directly availible
Everything that should be available to all users or installs to a public place should be installed by root. Everything else can be installed by a normal user.
Most applications are designed to run as a non-root user anyway, so it is not really a requirement to install everything as root. In fact there are very few technical reasons why something should be installed by root. It is mostly convenience and traditions. As others said, most packages install in places like /usr, /lib or other restricted places.
It is probably easy to create an "installer" user that can run a handful of commands via sudo to manage most installations.
The vast majority of the linux software is installed in directories such as /usr/bin and /etc where only root has (and should have!) write permission. Users can install (some) applications in the own home directory and run them from there. These applications are not autmatically added to the path of other users, and therefor not directly availible
Everything that should be available to all users or installs to a public place should be installed by root. Everything else can be installed by a normal user.
Most applications are designed to run as a non-root user anyway, so it is not really a requirement to install everything as root. In fact there are very few technical reasons why something should be installed by root. It is mostly convenience and traditions. As others said, most packages install in places like /usr, /lib or other restricted places.
It is probably easy to create an "installer" user that can run a handful of commands via
sudoto manage most installations.