Low fees is their secret I think because when compared to other exchanges here the fee is low and also some of the bigger exchanges had hacked at the time BInance grooming so people think that they have better security when compared to other so the binance going unstoppable in this very short term.
I dont think the fees is the factor which helped it grow so big. To be honest there are many exchangers out there with the same strategy as the Binance where they also offer you the discounts and perks for the holding of their ICO coins. Similar thing happened with the many ICO's but how many of them came up and used by the community ? I guess very very tiny portion. Binance is having better user interface than other crypto exchangers and thats what made it very very special in the first place. I guess if BNB would have been the typical one then there would have been no growth to it and its volume to the level which it did today.
May be the founder is secret himself who knows how to drive the bullet here.