Fair enough, you can do some sandboxing this way. But SELinux is not a sandboxing tool in the same way bubblewrap or landlock are. It’s a tool that can put gates around your tools until it’s a sandbox, but SELinux as sandboxing is not in the spirit of “tools doing one thing and doing it well”
You absolutely can sandbox using SELinux. Red Hat even has a tool called “sandbox” for just that: https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/selinux_users_and_administrators_guide/chap-security-enhanced_linux-securing_programs_using_sandbox
Edit: and Android sandboxing is built heavily around SELinux: https://source.android.com/docs/security/features/selinux
Fair enough, you can do some sandboxing this way. But SELinux is not a sandboxing tool in the same way bubblewrap or landlock are. It’s a tool that can put gates around your tools until it’s a sandbox, but SELinux as sandboxing is not in the spirit of “tools doing one thing and doing it well”