If we think of the financial system as plumbing, the central bank has direct pipes to banks but rarely to citizens. This is not usually a problem except when you need to do a big emergency stimulus push not having direct pipes to individuals means stimulus takes a long time to reach individuals (if it does at all). Even countries like the USA and UK had a challenge rolling out stimulus, so this is a mechanism to bypass traditional banking system in a crisis.
Thats just the banking aspect, the interesting stuff is what you can do with the type of money issued. For example you can build inflation into the currency, to encourage the user to spend it. Or it can be tied to carbon credits as a way to encourage the purchase of environmentally friendly products. I am not saying this is what is going to happen, only that a digital currency directly issued by a central bank has the potential to be used in ways that is not readily possible right now.