Artifact size difference

After yocto the generated core-image-base-raspberrypi4.sdimg image is of 1.1GB size. But when I create artifact by adding just 2 packages “sudo” and “git” in release-v.2.0, I get following artifacts :
a) release-v.1.0.mender (rootfs-image)
b) release-v.2.0.mender (rootfs-image)
c) v1.0-deltafrom-v2.0.mender (mender-binary-delta)
d) v2.0-deltafrom-v1.0.mender (mender-binary-delta)
as per Robust delta update rootfs. Here, I get much-reduced size for each artifact. How this much reduction, especially with rootfs?
a) → 56MB
b) → 68MB
c) → 95KB
d) → 5MB