It does not matter if the target site is yours or not. There are many possible uses and reasons why one might download an entire website. While we can’t predict or prevent a cataclysmic event of our favorite website, we can undoubtedly preserve them in their current form. This idea originates from the data hoarder community on Reddit, where the process of making archives for fun is nothing new. Sites get shut down, censored, acquired, re-designed or just lost.
Contrary to popular belief, not everything online is there forever.