I do not think that Coinmarketkap should remove all bad coins. Using this site it is convenient to monitor the situation on the market as a whole, but I don’t think that it’s good to analyze the graph of a particular coin.
Removing those crap coins means we can't track them anymore. Better to see how they are performing in the current exchanges. At least we have some reference to check about them. And also, someone needs to do double check or triple check for a particular altcoin, they are not oblige to fully rely on what CMC is providing them. For me, it is a mere guide to check those altcoins in the market.