Because he's innocent. Read the 2000 page unsealed documents. The journalist Sharon Churcher is the one who created the false charges for a book deal.

From page 805, 806 footnotes:

A telling example is a series of emails between plaintiff and reporter Churcher when plaintiff was working on negotiating a book deal about her alleged experiences and Churcher was trying to help her. On May 10, 2011, plaintiff tells Churcher she cannot remember whom she had told Churcher she had had sex with. Churcher responds responds, “Don’t forget Alan Dershowitz,” which Churcher says is a “good name for [plaintiff’s] pitch” to her literary agent. It is clear neither Churcher nor plaintiff believed plaintiff had had sex with Professor Dershowitz, since (a) Churcher suggests that he would be a “good name” to “pitch” because of his prominence (“he [represented] Claus von Bulow and a movie was made about that case…title was Reversal of Fortune”), and (b) Churcher states, “We all suspect [Professor Dershowitz] is a pedo[phile] and tho no proof of that, you probably met him when he was hanging put w [Epstein].” Menninger Decl., EXHIBIT.OO, at Giuffre004096-97 (emphasis supplied).

Also if you read the depositions, she's also the same journalist who tried to create the Trump's story and Guiffre pointed this out during the deposition that Sharon was making up stories for her articles.