A motorcycle engine is tuned different from a car engine. The compression ratios are higher and the valve opening times are longer. The injectors are tuned for more fuel intake and the exhaust is, usually, shorter and simpler than a car. So, if a 900cc bike produces 100bhp a similar size car engine will produce 45bhp to 55bhp. Additionally a typical 900cc bike will weigh 220kg but the same car will weigh around 500kg. You see a bike power/weight ratio is 100/220 and the car is 55/450 the big difference also means faster acceleration, bike 0 to 100kph about 3.8secs, the car about 14 secs.
Moreover A car engine is generally expected to work smoothly, require little maintenance, and be absolutely dependable and cost-efficient to make. These characteristics are normally not compatible with the high power delivery of motorcycle engines.