There are two kinds of background checks. The official kind done by a dedicated team with access and knowledge to retrieve city, state and federal data. And the HR kind, where someone without an investigative background and education spends ten minutes doing web searches and online "stalking" to see if the candidate has any untoward elements in their past.
The first kind costs hundreds dollars per candidate. The second can be done for about twenty bucks worth of time. You can guess which approach most companies use.
It's easier on most candidates, too, because a real background check requires them to fill out paperwork. An ad hoc one they may never know about...unless they fail.