You have a point since there are still people who want to exchange their coin for their fiat, but what I first understood was what if it is globally accepted, meaning all stores accept all types of coins, you can transact and pay using crypto and send money to, but still crypto is not our main currency it is still our paper money, so we still might need to exchange this in the future but can you imagine the future ahead of us like the possibility now is higher than five years ago in cryptocurrencies because stores are now accepting bitcoins as payments and countries they are getting legalize the bitcoins and as its legal tenders.
In addition to using exchanges to convert between fiat and cryptocurrency, exchanges also provide a lot of other services such as staking, trading, listing new projects...In the absence of an exchange, where would traders be able to make a profit?
Although we do not recommend storing your assets on exchanges, nowadays there are many people who take advantage of exchanges to make profits through the staking service that exchanges are providing. In general, exchanges have a lot of benefits that we need, not only to exchange fiat and crypto with each other.