Mods: No Time Capsules Without A Treasure Map by Menaceman44 from Mod The Sims.
This mod alters the chance of finding a Time Capsule when using the Dig interaction on rock piles to zero. If you want your Sims to find Time Capsules now you will have to wait until they find a Treasure Map and use the Dig for Treasure interaction instead.
The chance of finding a Treasure Map has been left as it was. It feels acceptably random to me.