One: The lake that feeds the fishery doesn't have nearly the water of the fisheries to which you compare it. That makes minimum flow, etc. far more difficult.
Two: Any management discussion must include Southwest Power, the quasi-governmental entity in charge of electrical generation.
Three: The Congressional resolutions that authorized the dam building did not include recreation or wildlife in its priority lists. As a result the Corps is duty bound to ignore those factors and the lands and water you are discussing are Corps.
Four: The grade between the Beaver dam and Houseman is less than the other locations, which means when water is off the water stays put.
I understand everyone's desire to upgrade the section to the level of the others, but the task will require enormous coordination of a serious political effort with a serious environmental effort. In the current political times, that is doomed. Furthermore, even if successful, the results will not be dramatic as the stretch is rather short and flat.
As a side note, there are many, many trout down in the lake. That is where many of the stockers go to grow large.