Here assuming you are referring to interdimensional beings - they did not solidify because they were not inhabiting/occupying physical bodies, which solidified the same way that the Earth did. So in essence, the 'beings' - if by these you mean beings in heaven or creators - locked themselves out of this reality, because they never fully embodied a physical body on Earth.
This interview explains this solidification process in detail as well Spirituality - Astral Projections in Detail
and this one
Reptilians - Secret Agenda to Prevent Self Realization (Part 1) - Part 113
for further details and explanations.