> I've always wondered why only Linux can do 'true' containers without VMs.

Solaris/illumos has been able to do actual "containers" since 2004[0] and FreeBSD has had jails even before that[1].

[0] https://www.usenix.org/legacy/event/lisa04/tech/full_papers/... [1] https://papers.freebsd.org/2000/phk-jails.files/sane2000-jai...