Author again: #3 is the reason they didn't do this ages ago. Now that they comprise a quarter of all music being sold, there's simply no way for the labels to walk. Even if they all agreed to, one could stay and reap the profits. If they managed to split all at once they risk being caught as a cartel (but they never could pull it off).

Apple essentially owns the most valuable market they exist in. They can't walk.

Read the article.