It is not Bittrex's fault for trying to make the majority of the crypto community happy. Bittrex's responsibility is an exchange, and IS NOT a code checker.
There is NO need to check the code. Just stop adding coins on the second day and give them a chance to prove themselves, that would weed out the scam developers. I wouldn't complain if there was 1 or 2 a month, but there's been too many to count recently, it's insane.