Also because they tend to light on fire, have next to no torque where you want it, purposefully burn a metered amount of oil, get crap mileage (which degrades relatively quickly to boot), ...

Eventually people tire of playing the rotary game, usually when they realize the weight savings and high redline aren't worth the numerous flaws on anything but a track car (and even then, only if you can live without much low-end torque).