My SSSS eScapades began when I was flying standby/NR on one of the majors. Every single leg of every single trip got the SSSSSpecial treatment.

I think part of it had to do with the fact that I couldn't get on the flight unless there were unsold seats on the plane, so I was a last minute passenger, and the boarding pass was issued at the last minute and only for a one way leg.

It continued when I began began buying tickets for a while, then I stopped flying commercially altogether for several years. More recently, I've rejoined the ranks of the flying public and have not had an SSSSS on my passes in a few years. I think the initial trigger was one way legs, last minute ticketing, solo traveler. Why they do anything is purely speculative on our part. Whether anything they do is effective is another question. I just live with it when I must.