Whether a system(d) service is activated by default after you install a package is a distro-specific choice. I know Debian and derivatives do, so it will be started at the next reboot; while Arch and derivatives don’t, requiring an explicit systemctl enable [–now] something.service to run it. The devs of the distro try to pick what they think their userbase wants and after the initial decision is taken it’s not a behaviour that can be changed lightly. Regarding running as root, sometimes it’s just the default configuration that can be changed to a dedicated user, other times it’s required by the privileges they use (e.g. if they need to open a port below 1024)