Just because something was financed by taxpayer money does not mean it should be free. It is definitely not a rule or how things work. Although I am curious what are the disadvantages of making it free, I bet there are some, even if lightweight.
Not sure how many patents are held in limbo by govt, but well crafted rules about just a sales tax on products that include govt patented techs could be a plausibly fair way to recoup research investments while making them free to innovation. It's somewhere between the way the (pernicious) RIAA/FACTOR collects royalties on music via surcharges on broadcast and streaming, old "shareware" licenses, and the viral aspect of the GPL, but instead it's via a sales tax.
It could be a unique case for opening up patent archives but then adding a niche licensing and import/export tax on products that use the govt patented materials or technology. Even though I think the idea of using taxes as incentives is fundamentally broken, and there is someting dystopian about universities effectively collecting private taxes through the patent system, in a case like technology transfer, it opens up the tech for innovation and doesn't collect until revenue and profit are realized. It's tax revenue a govt has actually earned by investing, so there is even a plausible libertarian case for it.