Why do guinea pigs stay still?

Because they like their house and its nice and quiet mostly.

Also because Guinea Pigs are burrowing animals that like to hide. If you see your piggy moving it's bedding around inside and around it's house, it's because it's a burrowing act & your piggy is acting like it would out in the wild. Sitting in it's house is it's way of feeling safe.

I have a variety of "houses"/hiding places for my piggies, & they love them all! The longer that you have your piggie & the more you handle it, SAFELY & SECURELY, the more comfortable your piggie will be with coming out and lounging in the open. Although they will ALWAYS prefer some "quiet time" in the safe zones. Sometimes tho, my piggies will nap right out in the open, lounging stretched out like nobody's business! But I handle them several times per day, and when they nip to go back home, I take them back right away - it builds the trust between you and your pet!