What are the reasons why corruption is worse than armed robbery?

"Better" is a debatable term, but I would have to say because the offense of robbery is straight forward... it either occurred or it didn't. Whereas corruption and bribery are much less straight forward and often require cooperation from participants or infiltration of an organization in order to prove.

Additional: It is noteworthy that robbery is a crime against persons, while bribery and corruption are crimes against property. The fact of the matter is that all the offenses mentioned are felonies and will net the perpetrator lengthy prison sentences.