One reason is that sugar has a pH of 7, while honey has a pH of 3.26 to 4.48, a killing field for bacteria. Also, bees process honey by means of an enzyme called glucose oxidase, AKA 'Penicillin A' (formerly) or 'Notatin', which reduces atmospheric O2 to H2O2 (Hydrogen peroxide), forming an antimicrobial barrier on the honey surface. Also, bacteria become desiccated in honey because of the hygroscopic effects of the sugar (mostly supersaturated in honey). Basically, related, but not a duplicate question.
Why is this question remaining closed?