Most start off as legitimate Companies but then go through restructuring, name changes, symbol changes, buy backs, stock splits, personnel changes etc. and along the way end up in the hands of shysters and conmen. At that point they are under the radar and can start the manipulation process, with a little help from the promo's, until they made their millions.
As you said by the time the SEC move in they have made their money and it's the poor bagholders that end up holding the worthless shares.