From some older threads regarding Arcadia competing at Arcadia.
The only year that Arcadia HS competed at the Arcadia Band Review was 1984. Southern California had a lot of rain that year, and I believe it was the Chino Band Review or another one that was rained out thus ending Arcadia's band review season very early.
...As the La Palma Band Review wasn't in existence, Arcadia's season would have ended at Chino. This is probably a big part of the decision to allow Arcadia to compete at their own event. Tom Landes and his students at Arcadia deserved the opportunity to compete with their peers in their shortened season.
Any talks of this happening again with the cancellation of La Palma?