I think that BTC and LTC are 2 popular coins that have existed for a long time and it could be 2 coins that are frequently used for transactions on them.
In general, content on the deep web (including the dark web) contains the following:

Selling weapons without a license
Child pornography
Selling malware, pirated software and hacking instructions
Selling illegal drugs
Sell stolen credit card information and user accounts
Selling fake documents and currency
Recruit killer
Gambling
Money laundering
Interior exchange