Even without the bacteria side of it, shoes are just dirty. You get dirt, mud, grass, rocks, and all sorts of things on them. I personally have removed my shoes at the door of my room for years, and when you look at my room's carpet, which has cats rolling around and playing on it every night, compared to my dad's carpet where the animals don't often go, his is much dirtier because he wears his shoes into his room.
Even without the bacteria side of it, shoes are just dirty. You get dirt, mud, grass, rocks, and all sorts of things on them. I personally have removed my shoes at the door of my room for years, and when you look at my room's carpet, which has cats rolling around and playing on it every night, compared to my dad's carpet where the animals don't often go, his is much dirtier because he wears his shoes into his room.