@RichBC It is unclear what criteria they had this time.
I speculate that they looked deeper in the coins:
how many people (polo accounts) are really trading the coins: 10, 100, 1000, 10000 ? Because two accounts can make a 100 BTC daily volume.
Have many transactions are made on the blockchain of the coin
how much work the tech support has with the coin. How many trouble they have with a stuck wallet or lost transactions. As this is costly for Polo.
This is my speculative opinion. Still I don't understand IOC delisting as they had a 8 Million Market Cap... Maybe my first two points applied.