Can someone enlighten me as to why a school district would deem WISC-IV scores inadequate for gifted placement and would only accept SB scores?

Our district used to use WISC-IV and now uses SB-V. They insist on administering the test - no outside testing. They used to let kids into the gifted program through means other than IQ tests (recommendations, other test scores, etc.) or with outside testing. Then, one day they realized that 20%+ of one class was in the program, and they tried to limit entry.

They probably read some of the studies that show kids who test over 130 on some common IQ tests often miss the 130 mark on the SB-V. While my DD14 did better on the SB-V than the WISC-IV, I think DD16 might not have made the cut with the SB-V (she took the WISC-IV). The tests seem to play to different strengths.