There are gas planets. There are solid planets. Why aren't there liquid planets?

It is possible that there may be exoplanets covered in liquids, much like gas planets are covered in gasses without a solid surface. It may be possible for a planet to be entirely covered by liquid over a solid core. It is possible that we may have discovered large water planets already. Such a planet would be covered by a giant ocean, with an icy mantle and solid core. Oceanic exoplanets probably tend to have Earth-like atmospheres. Water is one of the most common molecules in the universe.

Keppler22B is an example of such a planet. When diving down into the water on this planet, you would see a pitch black void because of the extreme depth of the ocean. Deeper in, the extreme pressures would cause the inner water to freeze into ice. Beneath all that should be a solid core.

Maybe liquid planets could be a transition between terrestrial and gas planets.