Very many people use their real details on those sites, even though the penalties of getting caught are much more severe.
The best example of this is Operation Ore - a site was taken down by law enforcement and many thousands of people were investigated and found to have images of child sexual abuse. The investigation was made easier because so many people used their real names and linked that to their everyday credit card, allowing easy linking to their current address.
https://en.wikipedia.org/wiki/Operation_Ore
One notable result was that Pete Townshed (of The Who) was found to have paid for access to images of child sexual abuse.
http://www.telegraph.co.uk/culture/music/music-news/9572773/...
> leading to 7,250 suspects identified, 4,283 homes searched, 3,744 arrests, 1,848 charged, 1,451 convictions, 493 cautioned and 140 children removed from suspected dangerous situations[2] and an estimated 33[3] suicides.[4][5] Operation Ore identified and prosecuted some sex offenders, but the validity of the police procedures was later questioned, as errors in the investigations resulted in a large number of false arrests.[3]
7,250 suspect and 1,451 convictions is pretty significant.
1451 convictions is still significant, but we also still don't know how many of those might be wrongly convicted, given that a number of them were overturned and several people have won trials for malicious prosecution, and we don't know how many "got away" without publicity over their trials simply don't want to risk appeals or lawsuits over their convictions.
It's worth noting that the company the data came from had in fact been subject to so much credit card fraud that it was going out of business when they were raided. US police treated the data accordingly. British police did not.
Giving your real name/address/DOB/credit card to a site specifically set up for cheating seems like basically asking to get blackmailed.