Thanks for sharing these stories!

So, I believe the algorithm is responding to stories that are popular. I had one take off around three weeks after it was published - no boost though. It just seemed to gain popularity and so the algorithm showed it to more people. And it resulted in doing significantly better than one of my boosted stories. So the boost helps but some may still fall flat after a few days.

I think the key here is to just write really good and engaging pieces because they will be enjoyed by many even if they never get boosted.