Crypto exchanges are necessary but having too much isn't needed. There are just new existing and new exchanges being launched for their own purposes. They're competing for a higher rate which they make as a business. Exchanges wouldn't exist if they aren't earning through it. Instead of being confused, we must be wise upon choosing an exchange.
I agree with what you have said, but for me multiple exchanges is helpful too since different exchanges offers different prices of bids we can see who among them is worth investing your assets, and in my experience there would be a lot of possible instances about maintenace and unexpected delays if we are all having a single exchange it will take so much time to have our money or profit that we have allocate to it. Crypto community allows these different exchanges to exist since not every cryptocurrency have the same compatibility with one other with our desirable cryptos which I think is helpful too for us convert our prior assets to another crypto.