See this story for just $56,000 on LocalBitcoins (Michigan Man Charged for Unlawful Bitcoin Exchange) It's back in 2017 but still.
Most of these sound like people running a business (i.e. continuously buying and selling with markup), and that's where all the AML and other requirements come in. That also seems to have been the case here assuming no one's lying: https://www.morrisoncohen.com/siteFiles/files/2017_10_25%20-%20U_S_%20v_%20Stetkiw.pdf
He had the charges dropped: https://www.courtlistener.com/docket/6182321/15/united-states-v-stetkiw/
But the alphabay part and apparently also CP found on his computer could have complicated things. Don't have a Pacer account so can't access further details.