There was once a study to test the amount of "poop particles" (feces based bacteria) on everyday objects. The study consisted of putting objects in places that would be more or less likely to have feces and a control group which was isolated from any source of feces based bacteria to the best of their ability. The microbiologists running the study were unable to tell which group was the control.
This is written to the best of my memory and some details may be wrong but the meaning is the same
In graduate school I swabbed a public toilet seat and wiped the specimen in a Petri dish. My cohort swabbed the bottom of their shoe and did the same. The public toilet specimen grew virtually nothing. The shoe specimen grew the equivalent of a rainforest in bacteria.
I live in California. The only people I know who wear shoes in the house are those with neurological damage making it painful for them to walk around in socks, slippers, or barefoot. CRPS sucks.
Toilet seats are naturally smooth and bacteria have a hard time staying on the surface. Most public toilet seats have an additional antimicrobial coating.