Often times the reason for overloading keywords is the reluctance to introduce new keywords, as this can cause backward compatibility problems. Instead of adding a new keyword and possibly breaking existing code that may use that keyword as a variable name or a function name, an existing keyword that sort-of fits is used for the new feature.

While maintaining backward compatibility is good, this does make the language confusing. Static is probably one of the worst offenders, but I think that C++ especially has quite a few of these cases now.