A government would be responding to customer demand.
Sure, they could create a centralized digital currency. But the market might not want to use that, so what's even the point of spending all this effort making it in the first place.
Whereas a decentralized currency has features that sounds me customers want.
Currently, demand for cryptocurrencies seems indistinguishable from zero. At the same time, demand for government issued centralized money is quite large.
The word "rapid" on that phrase was an entirely different meaning from when it's used to describe the rate of change of cryptocoins demand.
A large market is a more stable market. Crypto may get large at some point (I don't see why they would, but I don't see everything), but today they are nothing. Thus, preaching that people massively want them is nonsense.
Sure, they could create a centralized digital currency. But the market might not want to use that, so what's even the point of spending all this effort making it in the first place.
Whereas a decentralized currency has features that sounds me customers want.