Several Reasons:
1- You can’t just plug-in code from one Engine to another, for both Legal and Technical reasons.
2- CryEngines tech and lighting model is massively out of date. They also don’t use a Deferred renderer.
3- CryEngine ONLY has a SINGLE light bounce from ONE hard-coded light source (the sun). VXGI (nVidia’s Solution) and DFGI (Unreals Latest Solution), bounce from ALL lights, and DFGI is almost free
4- LPV is a horrible, leaky and poorly optimized unscalable technique for GI regardless of implementation. It has a very narrow range of uses. It did the job for a while, but technology has moved on.
5- CryEngine isn’t giving out it’s FULL source code, they give out part of it (don’t believe what you read on their website), and it’s still a jumbled mess.
6- It’s just a terrible idea.