It&#x27;s a combinations of physics and resource economics. There is a theoretical maximum efficiency in any Brayton cycle, which is in practice limited by the maximum temperature at the turbine blades, which is itself limited by metallurgy. Improvements on that front come very slowly--fuel efficiency has only about doubled since 1960, has improved very slowly since 1990. Except for the recent cratering of fuel prices, these improvements in fuel efficiency have been more than eaten up by rising fuel costs.<p>But, hey that&#x27;s pretty much the entire world outside of computing. Did you know that a modern coal plant is only about twice as efficient as one from a century ago? Same thing will happen in computing too, soon enough: <a href="http:&#x2F;&#x2F;imgur.com&#x2F;NFysh" rel="nofollow">http:&#x2F;&#x2F;imgur.com&#x2F;NFysh</a>.