Being a mayor of a top ten city is more impressive than being the governor of some podunk flyover state.
This is simply untrue. There is a lot to be said for being higher up the chain of federalism. Governors deal with a greater variety problems than do mayors and they deal with them more directly. Mayors deal primarily with logistical and administrative issues and not with the more politicized issues on which the majority of people base their vote. After all "There is no Republican or Democratic way to clean the streets" - Fiorello LaGuardia
Not to mention that dealing with conservation and agricultural issues is a mandatory presidential qualification that mayors tend to lack.