The snail I have is most active at night, when the lights are off. I think I read somewher that they are nocternal (unsure).
I watch mine during most of the day he just sits on the side of the tank doing nothing at all. But once it gets to about 10 or 11 pm, I can see him moving all over the tank.
Thought I would assume like most other living moving creatures snails have their own personalities. You might have just got one that is simply put lazy.