All about the name. If they were to bundle any, it would be Beats. Because the name sells. How many average consumers have heard of AKG, Dennon and others, and how many of those average consumers that have heard of them can tell the difference in sound quality/clarity, and how many of those that can tell the difference in sound quality/clarity actually care about sound quality/clarity?
If they package a brand of earbuds that someone hasn't heard of, but is the best made, maybe that average consumer might think they're crap because they aren't a name they've heard of, and go buy a set with Apple, Beats, Bose or another name brand that they have heard.