This, so much.Motivation is a big factor when it comes to working out, and a lot of people just don't have the drive to do it alone. Sure, they'll start out strong, maybe even make it a few weeks, but then they'll slow down and eventually just stop altogether. And that's where gyms come in. All you need is the motivation to get yourself down to the gym, once there the environment where you are surrounded by other people working out and using the treadmills/exercise bikes makes it much easier to do your work out without slacking off.
Also, if you go with others you can get some nice social time while still doing something constructive. And you can assist each other with heavy lifts and such.