Bitcoin is also accessible and convenient so it will be easy for them to use it than fiat.
Fiat actually accounts for majority of illegal activities with Bitcoin being used for only a small percentage. Also cash is more readily accessible and convenient, it is also untraceable. I believe the OP was comparing Bitcoin with more privacy centered cryptocurrencies like monero and why Bitcoin is still preferred to those coins although the article did not offer much by way of factual evidence, I would agree to it as Bitcoin is more liquid and established than most other currencies, as an enthusiast I would rather hold my assets in
BTC, so same could be said for scammers.
Exactly, as we noticed of crypto exchanges hacking, the criminals hold their Bitcoin for a while on the wallet and they let years will pass.
They would still need to use other methods to obfuscate the flow of transactions, like by using a coin mixer, converting through an exchange despite the amount of gap time leaves a permanent print on the blockchain which can be discovered at any point in time.
I would like to know if the mixer service can do the mixing if the amount of bitcoins you want to mix is large ?
As I recall, Mixer service can break treceability if bitcoin are in small amount but it would be difficult to do it if the transaction was larger. I read it in an article.
On Chipmixer for example you can buy chips ranging to above 8
BTC, this is a pretty large amount and if split into different chips it is relatively easy to effect a much larger amounts than that.