The need to use cryptocurrencies on the Dark Web occurred when in 2010 The Flower's Market moved to TOR. In reality, this first market used insecure systems such as prepaid cards and credit cards.
In a short time, eight were arrested for conspiracy, international drug dealing and money laundering.
Contrary to what one might believe, one of the first cryptocurrencies to be accepted was Litecoin.
More precisely on the Atlantis market (which, however, also accepted Bitcoin) which was closed in 2013.
However, the markets that were soon emerging (such as Silk Road) definitively adopted Bitcoin.
What was the need? Obviously the anonymity and non-traceability of the transactions (obviously we know that this is not the case because the transactions are recorded on the Blockchain).
The other big advantage was that the wallet address was not associated with anyone (today with KYC it is a little more difficult to "wash").
Over the years there have been many arrests and dozens of markets have been obscured by the FBI, however it should be emphasized that many times it has been "mistakes" of the admin.
Not so much of the crypto's insecurity.
Which cryptocurrencies are accepted today? Obviously Bitcoin, however, for some years now there has been a great use of Monero (we know that the Monero blockchain is encrypted).
Litecoin continues to be used.
Other markets have also opened to Ethereum, Bitcoin Cash, Dash and ZCash.