I agree with you. I trust multiple stock exchanges and are trading only on them. I do not understand why we need such a large number of exchanges, because it is really inconvenient.
We need to have a large number of exchanges because that will help us to get more profit from crypto. But that is only for people who have good skills in arbitrage trading, and he can use the chance to buy low in one exchange and send it to another exchange which has a high price. That will be making another profit as we know that the price in many exchanges will not be the same. But still, there is a risk that we need to pay, especially if we are missing the time in the transaction.
Arbitrage isn't really worth it, by the time you get your funds transferred over it is already too late. Arbitrage is good for selling physical goods in different markets but not so much for crypto trading. Plus a lot of orders on exchanges are completely fake.