I think the motorcycle/scooter industry just looks at their market and decides not to put more expensive fuel saving technology in their products. It'd make the price of a scoot/cycle too high. Not to mention, there may not be enough room.
Even so, if one wants nothing more than GREAT fuel mileage, one can buy a smaller scooter and get it.
There is no small car that gets mileage equal to a small scooter. No mid-size car mileage equals a mid-size scooter, etc.
But I agree, I really like riding in my '04 Honda Civic in comfort in all weather -- getting near 40 mpg!