Such observation supposes that our timeline matches theirs (taking into account the delay due to lightspeed). We weren't capable of such observation until about a few decades ago, other civilization could have existed and vanished billions of years ago, or billions of years in the future, or are so distant that they're outside of our obserable universe (if they ever was within it).

Or energy is not such a big deal anymore once you've reached a certain stage of technological advancement, so it's not the right criteria.