Obvious scams are obvious on purpose, but not for the reason you’re suggesting. They don’t want to waste actual manpower on anyone smart enough to recognize a scam. So they make the scam obvious, and they know that anyone that does respond to it is in that small percentage of clueless or gullible people that the scam might actually succeed on. They’re not trying to play 4D chess, they’re trying to find the people that can only play 1D checkers.