Sincere question: how much of that is inherent to FPGA systems, and how much of that is due to them being a niche technology used in contexts where there power consumption is not a big issue, meaning that there has not been a significant drive to reduce power consumption?
I mean, it's not like the other types of electronics are inherently energy-efficient either: before it affected battery life people didn't care that much about energy-efficient CPU's. The current drive for more computation per Watt is largely driven by the explosion in mobile hardware.
It's inherent to how FPGAs work. Logic blocks are necessary but are kind of a heavyweight solution to emulate normal logic (and they'll result in a ton of extra silicon driving leakage up).
Perf/Watt has always been interesting as well, It's a major concern for data centers (worse perf/Watt requires more cooling which drives costs up).
I mean, it's not like the other types of electronics are inherently energy-efficient either: before it affected battery life people didn't care that much about energy-efficient CPU's. The current drive for more computation per Watt is largely driven by the explosion in mobile hardware.