There is a lot of reason but the main reason is to make money. Don't think of it really hard since there are more exchanges coming from the next following years. They all want to make money andtake advantage of the continuous increase in numbers of altcoins in the market. By that reason, it is enough for them to make new exchanges.
There's some truth to that. Unfortunately, the main reason for initiate a new exchange is not to make it better or safer. NO, it is a money making project. Sure, you invest some initial money and time into it, enough to make it last until you get enough customers, get some money and ditch.
So, I'm yet to understand why we need any more exchanges when we already have the likes of Binance and Bitfinex.
The very first response of the thread will give a better understanding about having new exchanges.
Whats the need of more cryptocurrencies coming into existence. If one has got the answer, then he'll understand the need of new cryptocurrency exchanges. Everything is tied to money, if cryptocurrencies weren't associated with money this could've never been this popular.
The market keeps widening and to meet the needs we're in need of more exchanges, even when we've got reputed exchange platforms like Binance and bitfinex.