China doesn't ban Bitcoin (holding, trading, etc) but they only ban Bitcoin mining, just like another misconceptions China's can control Bitcoin since they has over 51% Bitcoin hash rate.
In addition from other users mentioned above, another reason is :
1. Volatility, many people scared of volatility and prefer to hold Fiat even though Fiat always inflate, but it's more safe in price term.
2. Not tech savvy, most of people doesn't want to learn tech because it's hard to understand especially for old ages.
3. No physical appearance, they no have any idea what those number came from and just thinking it's only a random number that could be faked.
The term ban Bitcoin is just temporary, sooner or later we will see another countries will legalizing Bitcoin as legal tender and it makes other countries follow it especially the countries was successful after legalizing Bitcoin,