The game engine market is very, vary hard to crack. Engines can be integrated into a greater system (like Unity), or they might be standalone engines that have various APIs to hook them into popular programming environments. It is hard to generate revenue from it.
A partner company ported a 3D engine over to work with a few popular RAD tools (http://www.franklin3d.com). They do sell some units but I know its very hard to support. I mean, to give reasonable support for DAZ Studio, you need the basics. To support a 3D engine, you need to be an engineer.