Because they don't know what they are doing.

In any case, a proxy makes sense, just not for the reasons they give.

People are running these as a program under their admin permissions, right? That seems to be the root problem to me. Start with having it run under its own user and you could use firewalls and permissions and keep it siloed to some Home directory or etc that you just copy files to?

The answer is that they probably aren't aware of all these things.

The people building this aren't good at engineering reliable systems, as evidenced by the incredibly wasteful core premise of what they're doing.

Namespaces and cgroups allow for resource accounting and limited isolation between trusted processes. It is only through hard work and luck that they have been usable in the k8s/docker world.

To be 100% clear, namespaces are not a security feature in themselves, but can be used to run processes with reduced privileges and improved isolation, but not for untrusted code.

A few reasons.

1) Kernel features explicitly need to support namespaces, and only the portions that support namespaces have increased isolation, any syscall, socket family, etc… can provide an attack vector for the global kernel.

2) The methods to further constrain processes like LSMs, SecComp, eBPF system calling typically are not implemented by common container images and are difficult for users to develop and deploy.

3) User namespaces have actually increased exposure to user data, if protecting the system itself because of the proliferation of capabilities(7)[0]. Capabilities were designed as a vertical slice of superior(root) user functionality, and the contract is much different than people expect[1][2] We will have to see where things go, but as far as untrusted code, no containers/namespaces/etc… are not sufficient at all. There are just too many holes in the shared kernel and several socket() based backends that are used through netlink etc… Here you can see just how insane the number of default capabilities are granted to every user right now.

     $ grep ^CapBnd /proc/$$/status
     CapBnd: 000001ffffffffff
     $ capsh --decode=000001ffffffffff
     0x000001ffffffffff=cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,cap_wake_alarm,cap_block_suspend,cap_audit_read,cap_perfmon,cap_bpf,cap_checkpoint_restore