Simple -- Altman's against IPO which is the only way for the company's investors to cash out. Eg., Sequoia Capital's performance heavily depends on OpenAI's valuation and the firm's ability to lock in profit asap.

The Board's purpose is to protect shareholder interests (aka make as much money as possible for investors). They do not care about AI safety, transparency, or some non-profit nonsense.

Expect OpenAI to IPO next year.