My theory is this. Since RV2 really wants to retire, he will opt to go race in the less competitive MXGP euro series and save his body and mind a ton of stress.
He has 1 year left on his Monster / Kawi deal so he has to compete, so he is choosing to go race in Europe. Plus if he wins a Euro championship he still gets some sort of bonus I would assume and he will also get a pretty cool new mark on his resume.
I think any level of MX is abusive on ones body so my theory could be way off but I would say that there is no way that Kawasaki would rather have him in Europe than in the US.