This is, as others have previously commented, a lovely still simple shot. There is no doubt that you met the challenge. In addition there is nothing technically wrong. The question therefore is why didn't this do better.
I can think of two potential reasons. The first is the colour tones - these are a little bit flat across the image. The surface of the water allow very little scope for texture and depth. The second is that the composition, although simple, is not easy on the eyes. Nothing draws the eye in. the kink where the pole meets its reflection is somehow jarring to the eye.
I hope my comments help and Good Luck in future Challenges!
This makes me think of "stick in the mud" - an idiom used to describe a person who doesn't want to participate in activities. But I like the reflection, dead space, and rule of thirds.