The big FA opt in/opt out candidates represent a different set of requirements than a "good" player. Anthony, James, Wade...to a lesser extent Love and Bosh etc are not only interested in salary. In some cases their endorsement deals double or, in the case of James, triple their salary. Be advised of the influence born by the other party in these matters, the agent. The agent gets 5 to 10 to sometimes 20% of the endorsement mark up on shoes, beer and Chevy's.
In turn, teams are not just getting a player, they are getting a "marketing asset." When a star is signed to a contract the team gets a large revenue kick through numerous channels.
Finally, the NBA will benefit as a marketing entity with Kevin Love in a big market. In balance, the NBA will lose with Carmelo in any market that is not LA or NY.
For all parties it is best that Lebron James is playing for a well managed team in a large market. Also best that he is in the finals each year. If you're not happy about this follow some sport that does require television revenue to pay everyone, like division III collegiate sports.
I don't believe Chicago or Houston are "right" for Anthony, Inc. New York is best for him, except zen guy has a lot of work to do. LA is a shot and who cares as he will be the perfect Faker. He and Bryant can fight for shots...whoopee.
Are the Celtics a spectator here? No, they are assuredly a player. They have won a lot of games with Ainge and classified as a very well managed team. They have a strong market position in the pantheon of NBA teams and are not considered a liability by agents. Star Celtics sell a lot of stuff and are recognized worldwide, these are all factors.
Would James, Anthony or Wade come to Boston? Sure, if a title chase is guaranteed, the player, the agents, the NBA would be AOK with proven President, Ainge in place. Will they come here? Doubt it, but 'taking deals off the table" because you don't like a player is not what is done in the NBA....working a deal is what is done and Ainge has a seat at the table.