Your line of reasoning seems to be along the lines of "anything not forbidden is compulsory" which is not a good place. Having the choice to donate but not being required to is good.
And yes, I think that if OpenAI is choosing to include an entire copy of LibreOffice in their product, it is definitely the right thing to do to sling them a donation. Note that the moral thing to do is not always the required thing to do, or even the legal thing to do.
People will absolutely pay for things voluntarily if you ask them, without forcing them to.
[0] https://www.theguardian.com/membership/2018/nov/12/katharine...
In a nutshell - voluntary funding by readership. No paywall. You can read as many stories as you like for free, and donate if you want. It works.
> Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith.
It does! And they wish to get donations. There's a button right at the top on the site making that clear.
> In this case, they chose -- explicitly -- to NOT require any payment or contribution from anyone.
Yes, so what? It is true that they wished to not require payment. That is one of their wishes, but they have more than one wish. And if they required payment, that wouldn't be a donation anyway.