So you want to ban cryptocoins when only a fraction of them are used for ransomware.
Let’s apply that logic to other things:
To stop drug deals, all forms of cash have to be banned, even though only a fraction of cash is used for drug deals.
To stop people from being stabbed, ban all knives, even though only a fraction of knives are used for stabbing.
Let’s ban cars and airplanes while we’re at it.
And so on…