They clearly would like donations, but choose not to require any payments.
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.
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.