If you can't do calculus, extra time is not going to help you. Its not like an extra 30 minutes in a closed room environment is going to let you rederrive calculus from first principles.
The theory behind these accomedations is that certain people are disadvantaged in ways that have nothing to do with the thing being evaluated.
The least controversial version would be someone that is blind gets a braile version of the test (or someone to read it to them, etc). Sure you can say that without the accomadations the blind student cannot do calculus like the other students can, but you are really just testing if they can see the question not if they "know" calculus. The point of the test is to test their ability at calculus not to test if their eyes work.