[Klaus23]

> Why do you need Flatpak for sandboxing?

You don't, but as far as I know, Flatpak or Snap are the only practical, low-effort ways to do it on standard distros. There's nothing stopping flatpak-like security from being combined with traditional package management and shared libraries. Perhaps we will see this in the future, but I don't see much activity in this area at the moment.