What use do they really have ?
None
Seems like possessing them isn't illegal, but just about anything you do with them is.
Of course, because you're using something that is not yours to deceive for financial gain. The pure definition of fraud.
All companies seem to not want to talk about this and try diverting you to credit repair services when inquiring.
Credit repair services are also mainly scams, there is no such thing as fixing a credit miraculously or erasing debt or bankruptcy by paying a few hundred dollars, a few legit ones can help you with errors in your history when you have proofs that data is wrong or with advice to check on dubious numbers that you didn't notice, nothing else, most of them are just as shady as those bitcoin recoveries or Instagram unban services.
Even if you find a way to legitimately build a CPN score up with tradelines what purpose can it legitimately serve?
It's impossible so it would've no use whatsoever since we're talking about theoretically growing something that is not accepted anywhere.