I feel like you might be confusing value and valuation. A valuation is what you believe a company would hypothetically sell for.
Selling a non-profit for ... profit... is kind of directly against the whole point of a non-profit.
So I would say thinking of the valuation for a non-profit is weird as hell.
Something like the Salvation Army has value of course. Sure, if you could buy the salvation army, there would be buyers lining up for this well known brand with cash in the bank and lots of donations (or revenue if you want). So technically you could be talking about a 'valuation'. But selling shares of it in the hopes of propping up value and selling it again... like that is just a for profit company.
If you let non-profits do that, that is basically just the end of real non-profits.
OpenAI Foundation, the non-profit. It wasn't sold, isn't being sold, and nobody is trying to sell it. The "valuation" Musk is referring to must be the $$$ value that OpenAI has, that definitely can be sold. When we say something doesn't make sense, because it can't happen, and something real was misidentified, can we come back to the real thing? For everyone's benefit I'll assume Mr Musk was confused.
No need to play the "if you could buy" game with the Salvation Army, let's use the Girl Scouts.
The non-profit, Girl Scouts of the USA, their mission is NOT to grow a cookie production empire.
Its Girl Scouts Cookie Program is a business.
The Girl Scouts cookie business can be valued like any other business.
If you can sell a cookie, you can sell a cookie business.
And none of this is weird.
Please don't take this as criticism for how the Girl Scouts operates, but retaining the cookie program inside the non-profit is not actually the mission. If teaching entrepreneurialism to young people is part of the non-profit mission, they theoretically hold bake sales. The cookie business could at any point be sold or licensed, free to maximize its profits or whatever objective Girl Scouts USA or its new owners have, and its sale or licensing agreement would fund Girl Scouts USA's actual mission. There's nothing weird in any of that, or the Salvation Army licensing its brand to a for-profit company that sells camo shorts, hypothetically. There are a lot of good and honorable reasons to do these things, I'm not saying they should.
If a complaint is that a donation to Girl Scouts USA didn't go to expanding their cookie product lines, THAT is weird. That is what I see here with OpenAI. Someone that avoids talking about the non-profit's actual mission, because that's inconvenient to their argument, and sour they weren't part of the business potential that was spun off. Their mission is to develop AGI that benefits all of humanity. You can call that entire concept BS if you want, it is totally irrelevant because what the mission is NOT is to sell as many codex subscriptions as possible. How can anyone see what's happening as anything other than if can't have it nobody can?