That is unfortunately a far more common practice than it ought to be, and not just for USMLE Steps. I have seen that kind of behavior endorsed by residents and even attendings. In some very competitive environments, some people begin to act as though the agreement they signed to keep test material confidential is more like a suggestion...
I was appalled when I found myself the apparent beneficiary of such a practice at my hospital. Basically everyone who works in nursing at my hospital is eligible for a specialty certification exam after a couple years of working in the field. There is a hospital sponsored prep course, which we are strongly encouraged to take. The hospital likes to be able to advertise how many of its nurses have specialty certification. I took the course, and was really disappointed. It seemed like the information was presented in a very disjointed fashion, and that it focused too much on some very specific details of some diseases, while barely touching on the highlights of others. A week later, when I took the exam, I realized why the course had been that way. For virtually every question, I could recall having been coached, sometimes to such a degree that the wording of the question matched up with the way the presenter at the prep course had explained the topic.
I didn't have evidence, so I didn't report it. But when it came time to renew the certification the next year, I didn't. I just let it lapse. When our nurse educator asked why, I explained my concerns, and she, of course, denied that there was anything inappropriate going on.
I've since learned that for specialties that have begun to require recertification every 10 years for attendings, that similar "study groups" are available, and well utilized.
Cheating happens. All you can do is hold yourself to a higher standard, rather than joining the crowd by saying that well, everyone else is doing it so...