It also doesn't bother with a boot loader, since containers after all share the same kernel, there's no boot loader involved anymore. But in systemd we have sd-boot after all, which is a modern boot loader with many security features we need to work with. Per-container TPMs are also not really a thing.
Hence, in a recent systemd version we added systemd-vmspawn. It's a small wrapper around qemu, which has the point of making it as nice and simple to use qemu as it is to use nspawn.