Originally, Wil had no intentions of making the company go public because of three reasons.
One, he isn't really interested to earn more money as he was content with what he has. Not to mention, his current wealth is more than enough for even the next ten generations.
Two, he was worried that he wouldn't be able to play War Online in peace if the company goes public as he will have to work harder in the future to care about the company's net worth, share price, investing of other giant corporations, frequent board meetings, etc...
And three, if the company goes public, the board of directors will have more authority than in the present situation. They can even remove him as the chairman if necessary like how he did with Lu Heibei. But, if he owns everything, his words will be final and no one would dare go against his wishes.