[Chris2048]

Wait, lifeless and geologically inactive seem to be very different things, no?

Even the moon has geological activity. Anything big enough will feel tidal gravity forces at least, and that energy has to go somewhere. I would have thought the more relevant factor is whether the planet can "absorb" the energy like a rubber ball (I think it's Titan that has a thin shell over a liquid body that "flexes" as it orbits), or if the forces cause shifts in the solid body.