calculus is full of ambiguity. Not in a mathematical sense, but as someone who has recently TA'd a calculus class, I can confidently assert that no mathematics happens there. Mathematics is only unambiguous insofar as you can check your own work. None of those students would have been capable of that. They're just memorizing rules with many unintuitive caveats that are unintuitive either out of an absurd desire to restrict the curriculum, or because they are natural in the context of their proofs, but students are basically forbidden from seeing those.

Universities have decided that making calculus as capricious as possible serves their interests of having a weeder class.