Because the cost to OpenAI to make an architectural shift is far greater than the cost to a new lab to try something different, providing details is usually a net benefit for recruiting, building trust, getting acquired, etc. The lack of details is a poor business decision because it makes them seem untrustworthy.
I'm not advocating that they should open source their model, but there is already so much noise in the space and many bad papers that being cagey is a poor strategy for winning over talent, developers, etc.