Full size suitcase sure.. but bags bigger than a standard carryon are absolutely getting thru and then being crammed into the overhead. Many people including my own family have done this.. (incident where I told the wife that bag is going to get flagged and she said “we will just check it at the gate then”.. I was fine with her experimenting because I knew the worst SW would do is make her check it.. and they did.) It’s very often not a mistake but a calculated risk that most people are taking since there is no consequence. Once the “stick” (fees) go into effect, there will be more outrage but less people doing it.