Decentralized exchanges are... exactly not that. They only trade on-chain assets for on-chain assets. Fiat ramps are not part of what makes a decentralized exchange.
I wonder what entices people to execute hundreds of thousands of trades totaling USD equivalent billions in daily trading volume on these platforms then. Would you say that everyone using these platforms is basically out to scam others or get rich quick?
It's sad to see what has happened to crypto. So many scams and people using it as an investment opportunity. It will obviously never be able to replace fiat in it's current conception.
It sucks that this hasn't happened already. Monero pretty much just works, the technology is already there. People insist on treating cryptocurrencies like stocks instead.