Also, it's good to note, that producing that much power in a small device would mean that device is very, very volatile. There was some research I read about a long time ago to design a small nuclear fission device that would ideally replace batteries with a much more long lasting energy cell that also would greatly increase output wattage. Besides the obvious miniaturization issues, the other problem was that if that much energy is release all at once, such as from a drop or being in a fire or something else catastrophic, the explosion it would create would be significant and do a lot more damage than any battery not to mention the heavy shielding itself as shrapnel would be way more destructive than the explosion alone.
Take that and then think about people who are likely to use these things as weapons and you can't really sell that kind of thing commercially. This is one reason that for example, gasoline is not more energy dense which would make it way more efficient. Imagine if gasoline was as energy dense as jet fuel. It would mean way smaller fuel tanks and thus significantly less weight both of the tank and the fuel and thus more efficient cars. But the danger in widely selling jet fuel to consumers is significant.