> Ask your favorite well-known professor how many proofs of P=NP, the Riemann hypothesis, or whatever they get per week.

My PhD advisor actually works in an area that is related to complexity questions that are related to P=NP. So if he would get spammed a lot with this kind of papers, I am pretty sure that I would know. Similar statements hold for other researchers who work on the same floor.

You might object that even though they might work on questions that are related to complexity theory, they are perhaps simply not the people that an "ordinary crackpot" thinks of as target reader for their texts - in other words one has to know a little bit about mathematics to know that the questions these people work on are actually related to P=NP. I will not disagree with this objection.

You may also object that the respective persons are well-known and well-regarded in their respective community, but the general public is not so much aware of them. I also will not disagree with this objection.

Nevertheless I strongly believe that if your claim were true in general, I would probably know.