I find it interesting that you guys are assuming it is the board acting out of greed and not the employees.
OpenAI was, shockingly, built as an open source non-profit. Under the CEO it became close-sourced and profit-driven thanks in large part to the investment from Microsoft.
You will note this letter says nothing about the "mission" of OpenAI. It does, however, talk a lot about reach and being in a "strong position."
Translation, $$$.
The board's letter does, however, mention its goal to serve humanity, and its role as a non-profit, while being extremely clear the board members have no equity in the company.
I find it very, very interesting that the employee letter mentions nothing of any greater responsibility.