A lot of the use cases of those curl | bash scripts are to support non-standard installation, like with unusual distros and user-only. And unusual distros are kind of an unsolvable thing, because people that want them won't want your package manager.
Typical "curl | bash" script requires root, as it want to write to your /usr/bin, /usr/lib and others. You could trick it with chroot, maybe. And maybe not. But in such case you should to discover all dependencies it needs hard way, as you need to put them in your chroot too.
A lot of the use cases of those curl | bash scripts are to support non-standard installation, like with unusual distros and user-only. And unusual distros are kind of an unsolvable thing, because people that want them won't want your package manager.