Why must the final sitting be repeated after a remembered omitted original Sajdah is performed?

Invalidators of Prayer, Part 3: Items 44–68 — Technical Cases

• Because the valid final sitting must occur after completion of the prayer's pillars.
• Because every Sajdah requires a new Adhan.
• Because the Qiblah changes.
• Because Wudu always ends after Sajdah.