Now a days exchanges offering their own coin for various purpose of use.This is one of the reason to drag people to your exchange. Bittrex and poloniex not offering any loyalty to their users. Although, they're still on the top 10 in my list of choice.
These two exchanges were legend in crypto, before BNB these two coins were the leading in the market in terms of volume.
Volume that time was below billions but because of the bull run last 2017 it has significantly rise, thise proves that it does not matter whoever comes first, the exchange that keeps developing will be more successful.