Wheels surface area is very, very small, compared to say a bike, tricycle or other wheeled vehicle. That's fine on hard smooth surfaces like say a roller rink or a skateboard ramp. But terrible on pavement and gritty surfaces.
Rubber wheels slightly deform and compress to meet the surface contours they ride on. Hard wheels like skateboards and rollerblades ...
You can use a 'negative' rake to increase the stability - like this:
It even works without handlebars:
Or if you want suspension too:
... sorry about the volume of the music!
The simplest answer to the question is "because the motorcycle gets in its own way"
Take a look at this picture of a trials motorcycle; it has perhaps the smallest of turning circles available in a motorcycle of a given length:
And here's a picture of a typical bicycle steering/suspension setup:
On a motorcycle, it's fairly universal to have the ...
I'll approach this from a different perspective to the other answers: Pushbikes have no limits on the steering range because they don't need to add the complexity and weight. They're simple, light, and traditional, so include only the features necessary. Turning the bars more than a few degrees while riding along at any decent speed isn't needed, bu it may ...
A bicycle usually weights about 18 pounds versus an average of 180 pounds for a motorcycle.
In tight turns a bicycle can easily be controlled by the rider shifting their body's center of mass as needed to nudge the bicycle to turn or correct extra overturning moments, by leaning in or out of the turn while playing with the handle bar.
The weight of front ...
Although there is a correlation between high speed, stability and limited steering range, I think this question is about low velocities. I.e. why even for low velocities, there is still not enough steering range for motorcycles. Therefore, IMHO, the reasoning that at high velocities need larger radii does not by itself prohibit greater steering range at ...