Interesting...I've read about the match being tanked and the gambling issues. it was "rigged", pardon the pun. People also forget Riggs had to defend the doubles court whereas King had to defend a singles court (not to mention the age difference).
The physicality of the game, and most games, is significantly in favor of men. For example, the fastest serve for women was 136 mph, for men 163. In fact, the 31st fastest mens serve is still 7 mph faster than the fastest woman's serve. In basketball, women only recently began to dunk. In men's ball, Jr High boys have been dunking for decades.
In the end, pro sports isn't sports, it is entertainment. Some people find women's tennis better than men's because men's has turned into a "ace competition" (meaning, its all about serves and little volley except for the french open). Same with BBall in terms of dunking and the art of the game.
In the end, most people pay more money to see men in sports than women and that is why men make more money.