Such an insane paperclip optimizing way of thinking. The marginal cost to serve static content is very low as well - if they really didn't want to pay anything they could give it to a third party.
So what is the value of the old forum posts? To whom is it valuable? Is there somebody out there who would be willing to buy it?
In case this isn't trolling, it's valuable to any users who have a question that was previously answered on the forums, and to any users who invested time and energy answering said questions. Neither of these show up as a revenue stream, but instead impact customer retention and onboarding - the absence of community support is a major negative when making a purchasing decision as a new customer.
These things are not monetizable but are foundational to monetizations. It's like office ceiling lights. You might as well forgo buildings and gather naked employees with laptops in parking lots from such perspective.
Things can have value without the need to bring money into the equation.