Why don't they reccomend to put neosporin on healing piercings?

It's been over 6 months let my belly button piercing is still having a hard time healing. I'm convinced that it snagged on sheets while I was sleeping because it's been acting up and being all puffy and red, but not infected. I've been doing salt soaks and tea tree oil (on occasion). I want to put neosporin on it but everyone says it's not a good idea. Why not? Now I'm curious!