Containers have some efficiency advantages but the way they are typically set up can use a lot of space on disk and eat up a lot of ram with duplicate services. Standard Debian or CentOS containers easily require 200-600MB of space.
Docker and other popular container management systems are oriented towards more enterprise scale operations where containers are frequently set up and torn down with automated cloud orchestration tools.
If we want to have a more PMC take on containers, what we need probably looks more like a few tiny linux matryoshka dolls. Alpine Linux is based on musl (instead of libc), Busybox (instead of GNU-derived toolchain) and OpenRC (instead of systemD) and gives us a bare-bones but very utilitarian base container image in just 16MB. We can, with a little bit of manual effort get this to run in a systemd-nspawn container.