They do it as a sign of affection. Usually because they think we're too slow/dumb to hunt ourselves.
I've looked into getting a Savannah F5. Not going to do that anytime soon, but very high probability I'll get one once I move. The main reason is, I'm somewhat allergic to cats, and savannahs for whatever reason don't trigger my allergies. Otherwise I'd just pick one up from the shelter that's literally across the road from where I work. Especially when it's warm, not uncommon to come outside and see 10-20 cats lounging around outside. Driving home from work is like an obstacle course. The little buggers know there isn't a chance in hell of anyone here driving over them, so they kind of lost their fear of cars. Not a very good thing in the long run.
