example, suppose there was a bug in openssl's prime number generation code. It will generate insecure keys.
No amount of sandboxing can help with that. The bug is discovered and the next day I run 'pacman -Syu' (I use arch, btw) and the problem is gone systemwide, except for any flatpaks or appimages etc. Those will only get updates (and stop leaking my data) if and only if its maintainer actually gives a fuck, is still alive and active. If not, you're sol