It's not clear that they are out to monetise, or they may not have made a FOSS engine to start with. Some (Godot, for example) have deliberately set up their ow

It's not clear that they are out to monetise, or they may not have made a FOSS engine to start with. Some (Godot, for example) have deliberately set up their ownership and governance structures to make such a source-available/open core pivot if not impossible, then very difficult.