many crypto exchanges appear

[OptimusPrime]

I saw the last few years, especially in 2016 until 2018, there were lots of exchanges, especially those that made coins themselves,
since binance successfully made BNB coins and exchanged them, so many exchanges appeared and made their own coins,
but what is the reason for many exchanges?

Reason for so many exchanges is to provide more liquidity to the crypto market.  There are many cryptocurrency exchanges but there are the best of them all. Not all of them will remain on the long term

[aldenlim]

I saw the last few years, especially in 2016 until 2018, there were lots of exchanges, especially those that made coins themselves,
since binance successfully made BNB coins and exchanged them, so many exchanges appeared and made their own coins,
but what is the reason for many exchanges?

Because crypto exchanges are a nice way to make a passive income especially if a person has the capability to manage or run a business
like that. The reason behind of all these exchanges are profits that they will make in this kind of money-making machine and everything is
all about money, let's be honest in here.
 

[Falcon]

In order to have much control of the project. Creating own token and exchange is much better than making a short sighted vision of the project. It is all about widening the project territory as much as possible.

[Hisbullah]

I saw the last few years, especially in 2016 until 2018, there were lots of exchanges, especially those that made coins themselves,
since binance successfully made BNB coins and exchanged them, so many exchanges appeared and made their own coins,
but what is the reason for many exchanges?

Yes I think so.  Many crypto exchange appear. Because crypto currency is more popular and will be the next fiat money.