Ask HN Mods: Why Do You Completely Change What Users Submit?

I recently submitted an item:

https://news.ycombinator.com/item?id=8052399

It made it to and remained on the front page for a while. Then, after some hours, ~180 votes and many comments, a HN mod changed the title completely and also modified the URL to a completely different article on a different site.

I understand that the new article might have provided additional detail (which another user had also indicated on the comments thread), but why is HN completely changing what its users are posting, while still attributing it to those users? It's odd to have something attributed to me that I did not submit. And, if the answer is that "the topic was the same", "the first article referenced the second", or similar, then it seems that editorializing to this extent wholly changes what HN is about. That is, why not just have users submit proposed topics for discussion rather than URLs?

And, what of any quotes or references to the initially submitted URL in the comments section?

BTW, on the one hand, it seems fairer to allow the user to keep karma earned for the article (as HN did), but this begs the question that if so many people had already upvoted the article, then might it have already been "sufficient"?