Bitcoin should not defend on exchanges because bitcoin was created before exchanges come into existence, there is no reason to worry if exchanges keep disappearing as long as you use them the way you are supposed to use them.
Bitcoin needs Bitcoin exchanges and exchanges need Bitcoin existence, between them there is a thing like mutual relationship. There were many big reasons why people in the past felt super excited with first Bitcoin exchanges, then Bitcoin Futures in 2017 and 2018 with CME and CBOE for example.
However there are many ways to trade Bitcoin, and exchanges are only one of available ways. They can trade bitcoin peer to peer, in person too.
Exchange have a sole purpose which is to be used for exchange of coins, and almost, if you use the exchange to buy and sell or convert your crypto to fiat only, you will not panic because you will not have your coins stocked in an exchange, instead your wallet should be a home to your bitcoin.
It's right but even people only want to use exchanges for trading, risk still exists. At the time they fund their accounts with Bitcoin deposits, they have risk of losing their bitcoins. Because exchanges can say they don't receive anything, the account broke exchange's ToS, and they don't allow user withdrawing that fund. Risk of losing your coins immediately starts and does not need to wait till one hour or days, weeks later.
Deposit coin, trade it, withdraw the fund after finishing that trade, it looks fast and perfect but you still have risk of can not withdraw the fund.
