dd 1x-2x is enough in most use cases. most people don't have the time to go rummaging through random hard drive to recover what is mostly garbage. there might be a gem in there, but it's a straw in a haystack.
People have stranger hobbies. I can certainly see the appeal of buying used hard drives just to see what you can recover; part technical challenge, part voyeurism, and part schadenfreude.
Back in ~2008 someone ran what they called "the great zero challenge" promising a prize to anyone who could recover data from a (60GB mechanical) hard drive after dd had overwritten the drive with zeros once.
The prize wasn't large, but the challenge got pretty good coverage on tech news sites, so it would have been good PR for any data recovery company.
Nobody accepted the challenge. I think recovering such data is impossible, and I'd be fascinated to be proven wrong - if you know anyone who could do so?