Moleworms refuse to make a burrow in the caves/ruins

Simple as that, they won't make a burrow no matter what, it seems.

While it's not that big of a deal, since cave's earthquakes bring a steady supply of them; ruins earthquakes don't drop moleworms nor rabbits. And since there aren't any rock-eating mobs in the ruins, that means that debri can accumulate and cause lag. It doesn't help that brought moles can get killed by the debri and rock lobsters will only stay near the entrance