Beats has a marketshare of something like 2/3 to 3/4 for headphones over $100 and annual revenue of about $1.4 billion in 2013 (1/6 of Facebook's revenue). If anything, $3.2 billion was a steal.
Citation required for such a handwavy assertion. Beats is a fashion brand and those are notoriously ephemeral. If Beats want to sell they may know the game is up, but then so would Apple.
You mention marketshare, but neglect to mention the size of the market. You mention revenue, but neglect to mention profits. For all your numbers tell me, Beats could be operating at a loss in a shrinking market.
And I'm curious: If $3.2B was a steal, what would have been a fair price?