Polar or flexible molecules tend to have a liquid phase also at low pressures, so do metals. Rigid, unpolar particles not (naphtalene, helium, iodine). The difference makes wether a not perfectly ordered phase still can have enough intermolecular forces to keep it in a condensed (=liquid) state.
A molten metal is likely still metallic. Hydrogen bonds in liquid water are still very strong. Dodecane is flexible, and methyl end groups can take up a lot of thermal energy without greatly changing the geometry. Etc.
Whereas naphtalene is too large to rotate the whole molecule in the condensed phase, but once you have enough thermal energy to break the pi-stacking, there is no other interaction present that could keep the molecule from flying away.
The better the interaction in the liquid phase, the less pressure is needed, resp. the larger the temperature range in which the liquid is the thermodynamically preferred state.