Grass might hold the cart in place, but most abandoned carts get dropped off in places where the wind can catch them and blow them into cars.
I did not usually see a free roaming cart though. Maybe times have changed. Usually, people would prop them up against a curb, or ditch them into a grassy spot, or they would put them by a low spot in the parking lot next to a drain, or put them next to a column on the sidewalk.
Just my anecdotal experience, it seemed like people would put their cart back if there was a cart corral in the center of every parking row.
I once calculated the number of carts Walmart has worldwide and it was mind-boggling.