What is the primary reason that subsurface oceans, like those hypothesized on Europa, are not dependent on the classical Goldilocks Zone?

Answer

They are kept liquid by tidal heating from a large gas giant.

Subsurface oceans rely on energy sources other than direct stellar radiation, such as tidal heating from a large orbiting body, allowing them to exist far outside the conventional HZ.

What is the primary reason that subsurface oceans, like those hypothesized on Europa, are not dependent on the classical Goldilocks Zone?
astronomyplanetshabitable zonelifeHabitabilitygoldilocks zoneliquid water