I actually find that strange, since in my experience the AI really likes to build energy. Was your sector set to Balanced?
Last game I played co-op with a friend of mine, I had almost all my sectors on energy focus due to the cost of keeping the fleet out of dry-dock for wars... And I ended up at like +80 food due to sectors. In fact I started building over most of my core world food tiles because it was just so stupid how much food I had.
Baffling to me is... when your empire is at +80 food, why the frick are the sector governors building orbital food modules onto the space ports? You only do that when you have a food shortage -- not when you have a massive surplus. Yeesh.
Right now I am playing a game with more core due to government and ascension perks and I am at 12 core systems, and about 14 worlds. No sectors yet. I am loving it.
Eventually when some worlds are built out, I will hand them off, but not before then.