its not block strength thats the issue in most cases, its the mass of the valvetrain and rotating assy. In lightening this, you reduce the wear life of the engine (how many 100k mile motorbikes do you see?)

If you built a big multicylinder motorbike engine youd be heading for F1 style designs and there is no reason why you couldnt have 15krpm in your car, but it would mean writing off your engine at 20k miles probably lol