Welcome to the new world of alliances.
These days airlines are loath to add new routes except where the financials are outstanding. They prefer to use codeshares or interlining to alliance partners. UA will argue, for better or worse, that their alliance with Varig gives them huge coverage of South America, just as they could argue that TG and SQ give them huge coverage through Asia.
If airlines were run by plane spotters it would be much different, but airlines are run by accountants.