easyflyer83 Sums it up.
I have only once seen an LCC boarding line checked for carry on size. I remember it clearly as it was so unusual. About ten years ago, we were boarding an EZY at BOD, everyone had their bag checked and much annoyance in the SLF. I can only imagine that an inspector of some kind was on duty. I agree that challenging some SLF about their bags would not be amusing and would, ultimately, delay the flight. Also, folks are able to put whatever they want on social media without fact checking. So they complain that the carrier took their bags off them or whatever. For the airline to find that and give a correction - they have to find the staff who were on duty and get their version. Of course, some carriers just ignore all customer nonsense and that can be the best answer.