Here's why. The companies that collect and sell these database records, and the hundreds of companies that re-sell this information do not emphasize the weakness of their systems. This is why they emphasize the words "instant" and "nationwide" in their promotions. Everyone wants cheap and instant as opposed to slow and expensive, don't they? Can you imagine a website that advertises "Slow And Expensive Limited Area Background Checks." In fact to get really accurate records in most of the country it still requires in person searching at each county courthouse.
These companies get records where they can get them for free; usually from a state's Department of Corrections, which means you are only getting info on a person if he/she has been convicted of a felony and sentenced to prison. When most people think of a criminal history background check they think of all arrests and convictions; both misdemeanors and felonies and the court disposition, guilty or not guilty and the sentence. As you can see, if you are getting only felony convictions, you are getting only a small piece of the pie. For example; a person could be arrested a couple of times for having drug paraphernalia or a small amount of drugs in his or her possession. If the records you are getting only include felony convictions, you would have no record of that person's drug abuse.
