I'm not sure if this is something that other people experience or it's just me but I tend to be way less "physically active" at home during weekends rather than when I go to the gym.
Except the fact that I can use the machines the gym has, at home I have some pretty basic stuff like 4 Kg handles and a carpet where to do push-ups, abs and other stuff, but I find myself being lazy even on the exercises that really don't need machines at all.
Plus I noticed that I get fatigued earlier at home when during repetitions, could it be the small room + my sweat + hot air? I really don't know but I'm nowhere as active as when I go to the gym.
Something else that might play a role is the "competition factor". At home I'm alone and I can watch a die-hard movie or put up some metal music but I'll never be as "competitive" as when I go to the gym. I'm a highly competitive person and I think something that greatly motivates me is to "compete against the others" when doing exercises. It might be silly but it's an hypothesis on something else that might stack up when doing exercises at home vs going to the gym.