Matches come from the tags Steam players vote on each game, weighted so a rare tag counts for far more than one that sits on half the store. A game's popularity never moves it up this list.
The closest matches to Polylithic on Steam are Flotsam, Colony Survival, Castle Story, Timberborn, Drake Hollow. They rank highest because their Steam community tags overlap most with Polylithic's, and shared tags include Colony Sim, Automation, Early Access.
How are games like Polylithic chosen?
Every game is described by the tags Steam players vote on it. Rare, specific tags such as Colony Sim, Automation, Early Access count far more than catch-all ones like "Indie" or "Singleplayer", and each game is scored on how closely its whole tag profile matches Polylithic's. Popularity never affects the ranking.