Also almost all governments have KYC/AML/CFT regulations that apply to crypto exchanges as well. And governments can monitor, control, sanction your bitcoin transactions by controlling these exchanges through regulations. When the local currency becomes unstable and the local government becomes unstable, one should assume access to crypto exchanges like coinbase will be very very hard.
But then, the seller has to pay taxes - either business taxes if it is a merchant or capital gains taxes in case they sold an asset. And taxes are paid only in Fiat. So you still need Fiat integration somewhere.