Why was the rotary engine by Mazda dropped and never taken up by other manufacturers?
The rotary/Wankel engine is quite a clever piece of kit, but there are two flaws that became especially evident in the well-known RX-7 and RX-8…
The rotary engine is notoriously unreliable. The design of the engine is such that it works in a very precise manner and is quite intricate. A common problem is the apex seals on the rotor tips wear down quickly because of this, and replacing them is not an easy or cheap task. Lots of disassembling is required to replace them… and there’s also a lot of other common issues. Engine rebuilds at as little as 100,000 kilometers aren't unheard of either.
They’re not exactly famous for stellar efficiency either. The Mazda RX-8’s 1.3 seems to get around 5-8KM per Litre… pretty thirsty. They also demand a lot of oil and have a very frequent servicing schedule; many owners of the RX recommend changing the oil every 3000 kilometers.