Hydrogen peroxide is a more robust inhibitor of bacterial growth than 70% isopropyl alcohol and betadine. however, isopropyl alcohol and/or betadine are used to prepare skin prior to surgery but hydrogen peroxide is not. why might this be?

Because it destroys healthy skin cells.

Explanation:

Hydrogen peroxide is an antiseptic that is more potent than 70% isopropyl alcohol and betadine but even then it is not used by doctors because it has a damaging effect on skin cells.

Our cells contain catalase enzyme which reacts with hydrogen peroxide and release reactive oxygen species which cause cytotoxic effect. So applying hydrogen peroxide on the wound to clean it destroys the cells and delay the healing of the wound.  

Therefore due to damaging side effects of hydrogen peroxide on human cells, it is generally not used by doctors.