Switching engines is a huge amount of work and there is simply no compelling reason to do it (no, "shiny water" is not a compelling reason). The game works and that in itself is amazing and incredibly valuable.
Crytek, unreal and source are all in the high 6 figures to license. I would need external funding, and once you make the jump to that level you have to ramp your artwork and content to a similar level. It's a whole different ballgame.