You may have guessed it right!
Because Of most people have their dominant hand as the right hand.
But There Is More to it,
See This Gear-Less Scooter,
Now Take a scooter looks from the side
You Can See Everything on Left Side.
There is another reason why the left-handle is a dummy.
When you try to mount a scooter on its stand, you grab the left handle, your stand gets engaged from the left side.
In doing so, you actually apply torque on the handle.
We know it, Not a good idea to apply torque on the accelerator if there’s no one on the bike.
The left handle is purposely made non-functional so that no one actually does something horrible while engaging a scooter stand.
Amazing how much thought goes into designing something that looks so simple.