TSA announced almost 18 months ago that it was phasing out the pilot freebie program which I presume you agreed to through UA.
You will need to apply for Global Entry ($100/5 years) or, if you don't have a passport - don't travel internationally, TSA Pre-Check ($85/5 years). Not quite just signing up, but not particularly burdensome.
You will still receive Pre-Check once in a while, but as time goes on, it will be less and less.