TSA needs 25 million enrolled so that they can cut the workforce significantly. Do you recall the long delays at checkpoints in the spring of 2016? What caused those delays was TSA cutting screeners (or perhaps a better explanation is not replacing screeners who left TSA) in anticipation of a huge rush to sign up for Pre. That rush never happened and TSA was caught short.

PreCheck is not about safety, it's about cutting the workforce.