IMHO they are looking on trading volumes and rare tokens that you trade. As I remember coin will add on CMC after 50000 USD day trading volume.
It's good that they have implemented this so pump and dump coins cannot get in easily, in the past, there are a lot of scam coins that have got in easily, that is the reason some of them are zero volume on Coinmarketcap, now that they are strict we can only sure that only the best coin can only get in their list, $50000 is such a huge amount and only legit coins can get that volume.