I wouldn't be too hard on the employees. I had to take retail jobs from time to time when I was younger, and it's a beating of a job at any big box store. Chances are the giant chains put the people back there with very little training, and a lot of them are honestly trying to do a good job. As for why they recommend S&W revolvers and Glocks, its because people seem to like them and they don't see many unhappy customers returning to send the guns in for warranty work.
I'm not saying we should give a 100% pass to big box stores who don't train their staff, but I think anyone looking to buy a gun should have done at least some research first. I learned long ago that trusting a salesperson's advice for any major purchase is a pretty good way to get a crappy deal.