If someone could claim exclusive rights: yes, it would be worth millions. However, we've chosen as a society to make IP law not apply to math and public science.

This is an extremely shortsighted view, just because you can't sell calculus, doesn't mean its value in general isn't titanic.

For instance, it underlies basically all modern science and technology, fundamentally.

The problem with putting a monetary value on something is always that someone either needs to buy it or sell it.

Since calculus already exists and is in the public domain, nobody needs to buy it. No government needs to invest money in it. (Assuming that calculus is a finished work for the moment).

This is, of course, not to say that calculus is not valuable.

A fundamental tenet of Free Software is that math cannot be copyrighted and that software is basically just math. Whether you agree or disagree with that, it's kinda pointless to approach the topic from scratch in 2019, it's been argued into the ground for like 30 years.

The value you get from something has nothing to do with its price. When people say "X is worth Y dollars", "Y dollars" refers to what they can sell it for, not how much "value" its adding to society.

Its not nearly as straight forward of that, think how many dollars calculus has generated.

Yeah, Newton's heirs have a huge check coming to them, when US Congress retroactively pushes copyright back a few centuries by extending it to "life + 300 Years".