My fault - I asked them to do it.
If you have your Display Mode set to Linear, it displays all the posts in a thread beginning with the newest one at the top. I find that the easiest to use, especially when a thread gets lengthy. For anyone using that display mode, allowing replies would have put the link and graph at the bottom of a bunch of replies that could have really piled up after a couple seasons, and I figured that would defeat the purpose of having the sticky in the first place. I figured it was better to have various threads about water level topics, like the one LundAngler started, but leave the sticky as a standalone link for people who just want to see the numbers.