I would love to consider crypto as a type of medium of exchange. Unfortunately, as soon as crypto came out, I saw governments of many nations moving into it in some way, shape, or form. They gave it two options, either government has full control over time or eradication, with a few outliers. The US SEC was vacillating on how to deal with crypto for quite some time, and they are not alone. Is it property or legal tender, both, or neither? Now they have planted their stake.
Cash is a tangible and disconnected way for payment for goods and services. Disconnected, as in the government (mostly) does not have instantaneous method to cripple the existence of cash. It requires significantly more interaction than just disable, for our example a government run, centralized crypto exchange (lest we forget, however you feel about politics, when governments froze or seized banked assets).
1. fear of the government wiping out all crypto assets in an instance because one disagrees with them, or more likely by an accident or hackers.
2. no transactions can be conducted if there is no electricity or device to conduct the exchange of crypto. There are many nations where power outages are scheduled as a matter of fact, or worse, power on times are scheduled. The dependence on a device is a bit more acceptable but the cost between a paper clip that holds the paper cash versus a cellular phone is still enormous.