They will get people to use a CBDC by offering them a UBI that they can only receive and use in the CBDC.  Once everyone is switched over and using the CBDC, that is when they will start programming what you can and can't spend money on, when you can spend it and when it goes away, and shutting off money to those who don't act, speak, or think in the right way.  Almost everyone will switch to the CBDC to get their "free money".