Such planets would have to be small enough not to be able to retain a thick envelope of hydrogen and helium, otherwise they would form a warmer version of an ice giant instead, like Uranus and Neptune.
Such planets would have to be small enough not to be able to retain a thick envelope of hydrogen and helium, or migrate close enough to their parent star and be striped of these light elements. Otherwise, they would form a warmer version of an ice giant instead, like Uranus and Neptune.