I’ve never seen that before! But this is what I was meaning:

I knew what you were talking about. The drawback to those is they take up a lot more space since the slope needs to be gentler. As well as what you mentioned about carts sliding back down. Doesn’t even have to be many carts. Just somebody not paying attention, kids messing around, or a heavy cart that an elderly could manage on flat but can’t keep stationary on even that gradual slope.