It's a catch-22. The pinksheets have lots of foreign ADR's listed. Many small banks, large bankruptcy restructings, debt instruments issued by large caps, etc. There's close to 90,000 securities on the pinksheets. Shady penny stocks make up a small portion of it.
Rather than change or abolish the market, the SEC says buyer beware to those buying penny stocks. By doing so they're saying go ahead and hang yourself but remember we warned you. They've tried to at least make it more difficult and reduce liability for brokers by demanding that all penny stock trades be unsolicited, which means if you screw yourself it's you own fault.
Now that doesn't mean they turn a blind eye to shady pinksheet stocks but they only have limited resources so it has to be a slam dunk for them to go after a company. In fact, the SEC has never lost a case after indicting a company.