Don't forget Goto.
I wonder if Nakamura would have left if he got the HW title again. When he won the IC strap back from Goto I remember a quote from him like he didn't even know what else he could do with it
I think Goto hit a Nakanishi-like wall years ago. They never pulled the trigger on him and even if they give him a push it wont mean much. He's a good worker but has lost any chance of being a real star. He needs a Naito-like makeover and I don't see that happening at all with him.
Nakamura probably saw the writing on the wall of him being forever the 1B or 2 to Okada and Tanahashi. He's not getting any younger, knows the US audience loves him and is more receptive to him than any other current puro star, and he knows for a fact that even if his WWE stint is a complete flop, he will be treated like a WAY bigger star in Japan once he comes back. It's a win-win situation for him if he can avoid any big injury.