I am a mathematician, though I haven't been in academia for many years, and I would indeed be surprised if there were a lot of mathematicians who "just memorize

I am a mathematician, though I haven't been in academia for many years, and I would indeed be surprised if there were a lot of mathematicians who "just memorize proofs". Do you really mean that, and if so what's your evidence for it? (And: how do you suppose it is possible for someone who merely memorizes proofs without caring what they are about to prove new things in their field?)