Frankly, if one has made about 38 millions already - what good would be a contract for another 68? It all comes down to this: does Craig want to subject himself to another four to six years of a grueling schedule that takes most of a year of being in top shape, training every day, suffering through countless press junkets and premieres, while cementing that people only think of you in one role (which is acting-wise limited and will always remain so)?
I don´t think anybody can blame him. He has given everything he can, he was terrific and changed the perception of what James Bond should be like.
If he really has quit, I can only say: thank you, Sir, for doing a marvelous job.
Also, remember that in former times the rumour mill went on for years about whether Sir Roger would return, whether Timothy Dalton was done or even Pierce Brosnan.
It´s been six months since SPECTRE was released. Six months.
Should the decision be made official in the upcoming weeks it would be almost shockingly quick.