To add, the real height of the big-band craze was probably more like 1938-42. Records were coming out at a fast-and-furious pace. In 1942 was also when the Petrillo recording ban started (ending in 1944), which prevented records by big-bands, yet allowed the record companies to release vocalists’ recordings. Timing that with the wartime draft snatching up sidemen, gas rationing hampering traveling, and such, it was really crippling things even well before 1946. Seemed like bands were trying to regroup and get their mojo back in late-1945, but tastes had changed, and apparently this cabaret tax was also a factor.
The recording output of major-name bands in 1945 and 1946 (after the recording ban) was very tiny, compared to 1942 and before.
Looks like the unions were more responsible than the tax man.