It is because CMC generally issues aggregating prices, ticker data which are not providing per-market+exchange charts/data. Some of their competitors like https://coin.market/ provide such trades data, so you can calculate how much volume was for 1 second - so you can also check how many trades were to get, for example, btc/usd in a selected price range on all exchanges or on one exchange - it allow to easily avoid such faking of trade volumes from shady exchanges.