Would you put your shod or dirty feet on something others are meant to sit on?
Most of us have sat on a lawn, or a grassy field, and both have had plenty of dirty feet on them. So it has nothing to do with our sitting on something.
I wouldn’t intentionally place dirt on someone’s furniture, and sometimes I stand on chairs and sofas to reach high places.
It is interesting that Maori have a very strong tradition against sitting on anything that might have food on it. Which probably has a lot to do with pants not being part of their culture until relatively recently.