Well they have been and partly still are on the Tor network.
Discussion
Tor is often called the darknet. That's why the markets are called DNMs. DarkNet Market. Did you not see this: nostr:nevent1qqsppv0e09ncse8v2rdpgm9h975z4hrgeffzz9e5pl2e7zfuyv7mtlcpzemhxue69uhky6t5vdhkjmn9wgh8xmmrd9skcq3qyu7h0k3sqf065d37gzmpz4d0eq7ehamtw75n0s3n2lelmyhctt9qxpqqqqqqzl2hemf