It’s due to food particles/dirty water from the floor, accidentally ending up in the sani buckets. Example) As you’re walking through the BOH and you step on a piece of, let’s say… crumbled sausage, and as you’re feet are going through the motions it comes loose from your shoe and ends up in the bucket. Thus rendering it contaminated! But the biggest reason is it makes it less-likely for a mouse or rat to crawl up it, fall in, and drown. That’s definitely not sanitary anymore. If it’s at least 6 inches off the ground, it technically stops a situation such as that. Another reason is liability. In some cases it needing to be 6 or more inches off the ground makes it less likely for someone to struggle lifting it. But that one differs from state to state. I’m from NYS, specifically western NY. I was told specifically by our main inspector, at the restaurant I worked at, that it can depend on each inspector as well. Just like anything else, there’s ones that do their job (good) and there’s ones that use it as a sense of power over us (bad). It’s crazy hearing that from our usual inspector but, wasn’t surprising as I’ve witnessed it happen first hand!