I have to agree with the TSA that carrying more than $500 or so in cash is definitely suspicious. Usually a sign of drug trafficking or other illegal smuggling (but most smuggling is in the drug trade), or possibly counterfeiting (although that's unusual).
Nonsense. Carrying a large amount of cash is a sign of nothing other than carrying a large amount of cash. And $500 is peanuts if you're going somewhere where credit and debit cards aren't in much use.
If you're going somewhere like that with more than $500, such as Somalia, you're also probably going to be murdered and robbed, so it all works out. That is, unless, you're a local warlord.
