Let's first define what a loader and bootstrapper are in actuality.
If you decide not to use UnturnedGuard Bootstrapper and choose to install UnturnedGuard manually, the issue is that you will have to install an entire archive while also including Libraries and Plugin for each new update of the UnturnedGuard. The main purpose of loaders and bootstrapper is automatic update or installation of something, in this case UnturnedGuard.
The user only needs to restart their server or enter a command to install a new version for the operating server, which actually resolves a lot of issues that developers can repair quickly.