[zobzu]

debootstrap just populate a directory with files from the debian/ubuntu distros, LXC uses it, everyone who wants to create/boot a debian image that they create use it.

One major difference between systemd-nspawn and LXC is how simple and reliable systemd-nspawn - in particular the guest OS/image has to run systemd as well which is what provides the integration.

Eventually, if you wanted, you could mix and match the tools just fine.