Not just temperature, but pressure
The boiling point of a liquid depends on both.
It's how they "freeze dry" coffee without boiling it - remove the water by allowing it to evaporate in vacuum.
The universe is full of water molecules. Sure, a lot of the local ones are bound up in ices, but as soon as they get warm enough -- such as when a comet approaches the sun -- they sublime directly to vapor without passing through the liquid phase.