One day I was using an adjustable bench at one of the gyms I work at to do incline db curls. I had my intra workout drink and water on the pillar about 8ft behind the bench because I hate leaving my stuff on the floor because inevitably someone kicks the shit over. Now there were 4 other benches right next to the one I was using. Mine was the only one set to an incline. I get up walk over to my drinks and when I turn around a member just had to choose my bench to do concentration curls at. I just shake my head and go to the bench right next to him and adjust that one to the same incline and start my set. You'd think maybe he would realize since I had been standing over there near the benches and that once he sat down I then had to adjust another bench to the exact same settings that maybe I was using that one? Nope. And to add insult to injury he was cheating horribly and those concentration curls.
Aside from pointing out how inconsiderate most people are, my other point is as an employee I always just modify my workout if someone is using a piece of equipment I was on or was going to use.
Most commercial gyms are way too busy for people to be doing any type of circuit training, especially when it involves a journey around the gym for every circuit. At most I will superset two pieces of equipment that are near each other and sometimes that shit doesn't even workout.
I think part of the problem is these people get so set in doing the same shit day in and day out that they don't know what else to do, dare I say not educated enough in exercise to figure out any alternatives.