Present-day skateboards are actually engineering marvels, but they have been so refined that they are quite simplistic by today's high-technology standards. Perhaps this is why they work so well in that they keep it simple; a founding principle of good solid engineering. There is not much to a skateboard once you have the board, the trucks and the wheels, everything is pretty straight forward. The boards are made out of plastic, would or composite materials. The trucks are made out of combination of alloys and the wheels are made out of urethane.
Not only are there few parts, but the manufacturing allows for some stiff profits by the time the brand marketing techniques are applied to the teenage consumer mind. Everyone wants a "rad" skateboard, did you when you were young? I know I did. Perhaps why the skateboarding industry approaches the billion dollar mark during peak 10-year industry sub-sector cycles? Some say that high fuel prices increase skateboard costs as the parents are less willing to drive their kids to various activities in the gas-guzzling SUV or mini-van?
Hoverboards are quite a bit more complicated than actual skateboards. You see, hover boards must have their own propulsion system and a radically new design to be able to fly. A hover board by itself is fairly easy to make, but making one which supports a human being is a lot trickier.
For a very small board to lift up a human being using current technologies is not completely impossible but the board must also support its own weight, motor, blowers, electronics and fuel before it is ready for the human rider. Even if the unit is powered by a battery, batteries still take up weight.
Making the hover board very light is a must, but there's only so far you can go before you hit a hyperbolic curve of diminishing returns. It would be nice if the skateboard riders did not weigh so much and if they would lose a little weight, but we cannot count on humans to watch their diet judging from the current obesity of American societies.