CBDCs would grant immense power to the state. They would know every purchase you make and have the ability to block specific transactions or even freeze your account fully. It's an authoritarian's dream.

Stablecoins have drawbacks too, and the state could exercise control over them somewhat. But blockchains have more property rights and privacy (although not total privacy) built into it by default. It would be much more difficult for a state to overcome those hurdles.