The USG has deliberately kept some known or suspected terrorists off the no-fly and other aviation watch lists, supposedly so as not to alert some of them that they are known or suspected terrorists or so as to have a USG-working relationship with some of them.
Even putting that aside, why is it any surprise that various current or former terrorists currently free in the US would end up with PreCheck LLL sometimes? As long as they are screened for contraband WEIs, their getting PreCheck LLL doesn't bother me; rather, I find that PreCheck LLL type screening at the airport should be the default screening standard for passengers in the main.