HBO shows that you can be a la carte and successful.
HBO and sports are not even remotely comparable in this manner. If you live in New York and like the Yankees, chances are you'll see them on local or regional programming. Another large portion of revenue is tickets sold for fans to sit at the game. The more people you allow to watch the game at home, the less money the team makes from tickets. Eventually even the hot dog vendors lose their jobs.
Now take HBO. They have contracts with studios and do not pay for the creation of 99% of the programming you see. They have costs for their own investments and they do pay the studios for the rights to show their movies but they do not pay the $x millions directly for the filming of those movies.
HBO is also not governed by the FCC is the same manor as regional sports. The reason for any sports subscription is the ability to get around the FCC. Being on the west coast and wanting to watch an east coast team creates problems with basic programming. Being able to pay for a subscription directly for MLB, NBA, NFL, NHL... is the work-around and is basically the al a carte that you are refering to.
The overall difference here is HBO is one type of programming(for the most part), movies and original series. Sports is much more vast. What part of the country are you in? What type of sports are you looking for? Is it college, pro or high school? Do you need to pay for the channel or is it on a local affiliate? Even if you pay for the Sunday Ticket, if a game is being shown on your local or regional channel it will be blacked out on the NFL package. This is so the game can be sold twice, once to a channel holder and again to the nation.