Heat also plays a big part in motor application. Like was mentioned earlier, a scooter/bike motor tends to have a lot of metal to soak up and eventually dissipate heat. Compared to RC airplanes and cars they get relatively low airflow and high load.
These tiny little high revving RC motors you see have very little metal making them incredibly light weight. In an airplane they basically power a fan blowing right back on the motor at 50 mph+ 80ish kph. so they can run wide open throttle(WOT) no problem. RC cars and airplanes weigh less than most wheel sets so the load is very small resulting in less heat to begin with.
You need a gear reduction unit for RC motors in Ebike applications. Skateboards work great because of small wheels. Bicycles and scooters have big wheels. A gear reduction unit makes cooling very difficult.
EDIT: I would most def avoid that skateboard unless you can try it. That thing is at least 50lbs/23kg ish.