Mind you. Yao has been working hard every season and improving

So, I don't know where you got the impression of him just working hard for one season.

You have to realize that any great player needs to work within a system that suits him. As it is, this system ain't working well for Yao, as evident in the past two months.

Also, I need to remind everybody, even a great player like Magic Johnson requires a system and great players around him to make him earn that ring, then the next one, the next one.... NBA and TVs have glorified and and magnified the role of great players, the last shot, the last block, etc....that's fine. That's TV and entertainment. But the hard core of winning is still the system, the players who can complement each other. Phil Jackson's books made this point really clear.
Yao ming doesn't have that in this system. So, either they change the players/coach, or he changes a team if he wants the ring.

The key: the goal of YM is win one within a system that suits him. Hey, he is no Superman, and nobody is.