Maybe we should have easy to use sandbox commands controlled by the user. Currently all the software must be designed and compiled with sandbox restrictions deliberately (e.g. Chrome). It is better if we can sandbox arbitrary programs with convenience.
Don't we have that? With SELinux, sandboxing is literally a command away (and the command is, aptly, named `sandbox´).
There are certain inconveniences when it comes to sandboxing applications, especially applications that require an X server, which is why sandboxing is not done by default on any popular Linux OS.