Maybe because it is very complex to convert the money from crypto and it requires KYC where personal details are required before getting the money.
So they prefer the traditional thing and besides not all of them are capable of hijacking cryptocurrency.
It's obvious that it's easy for criminals to use the traditional which has easier transaction processes.
This is what i do have in mind where converting your cash to crypto will really be having that kind of problem on someone who do tend to make out conversions throughout to exchangers
which basically means that you would need up to pass some KYC before you would able to do so which criminals doesnt really like this kind of thing of course.Unless
if there would be some p2p purchases then they might able to get some bitcoin but in most cases this would really be on exchange platforms.
Why would they dive into things that will put up some headache if they can just simply make use of fiat directly just like the good old ways.?