Why did the rotary engine fail?
The rotary engine is considered dead because of very poor design, poor fuel efficiency, very poor emissions, high oil use by design, poor combustion chamber sealing, problematic of no starts , low engine torque. The nature of the design is too much to over come the majority of it’s issues. The rotary has never been explicitly banned, the alignment to f1 was the only reason it wasn’t allowed, much like many of the piston engines that had been racing at the time were no longer allowed.