Just because a system or process becomes more efficient, doesn't mean
it consumes less energy. In fact, it's possible that when it becomes
more efficient, it leads to an increase in demand.
Notable Examples:
Google SERP webpage optimization (pages were more lightweight) lead
to an increase of server load. Suddenly, people from NBU
countries were able to access the pages that they weren't able to load
before.
Solar/renewable energy has been become exponentially cheaper. Thus,
energy generation has become substantially more efficient. However, the
proportion of the energy grid that renewables makes up has remained more
or less constant for several decades because energy demand has also
grown at similar rates (via the
superorganism paper).
When cars in the US (or, at least, California) were mandated to
become more efficient — either by fuel economy or electrification — they
also, more often then not, became physically bigger. The electric
hummer, for example, has the same carbon footprint as a gas-powered
sedan.