Some fans were indeed surprised to see talks about him wanting to leave the show, but until something is said on the official front, it’s probably a good idea to avoid making guesses about the actor’s motivation.
We don’t know what the situation is, after all, and we certainly don’t know what the stance of the showrunners themselves is. It’s entirely possible that things have reached a point where there is simply no reasonable way for the show to move forward while keeping all parties equally pleased, and it wouldn’t be the first time something like this has happened with a major TV production.
It the current season of “The Big Bang Theory” really is the show’s last, this would imply that things are going to move quite fast in the next episodes. There are still many loose ends that have to be tied up, and the writers haven’t really indicated that they are going to conclude those stories anytime soon.
On the other hand, they have introduced plenty of new developments to the plot, further indicating that they are planning to continue the story as it is. This has all been quite confusing for followers of “The Big Bang Theory”, and nobody knows what to expect from the future right now. The one sentiment that gets repeated quite often in the discussions of fans, however, is that the producers should not keep quiet if they really are planning to cancel the show soon.