Foot infections, in my experience, are just slow to go away. I think it is because of how their circulatory system in their feet works. In a way it is an advantage because infections can stay localized for a while, that buys time to treat it locally instead of worrying about systemic infection right away.
It has taken five weeks to get rid of bumblefoot in a few cases, here. Romy's first foot splinter took several days to completely heal.