The main reason is that Binance is really "customer focused". They are engaging the user in many decisions. For example are they doing a "coin of the month"-poll and the user can decide which altcoin should get added next.
IOTA for example got added after that poll. So they are keeping their promise and trying to improve from week to week.
They offer a 50% off trading fee if you use the BNB coin. This is a great deal for daytrader because you safe money while trading.
Furthermore you are getting every Bitcoin Fork which is happening in the crypto world. Bitcoin Cash/Bitcoin Gold/ Bitcoin Diamond and 3 BTC hardforks will happen on December.
So be fast and get your BTC to Binance before the "airdrop" on Dec 15th Bittrex and Bitfinex for example didnt give me the Bitcoin Diamond...
Binance also gifted all users 500 TRX through a Airdrop Bounty Program
And at the end I can say that they are doing permanently competitions for the user with good winning prizes and I guess that they will add many things in the future as well.
For example are these 3 competition running right now:
