The first reason–the obvious one–is to discredit and financially damage the heart of the vast right-wing media conspiracy: Fox News. The second one is to make it clear to the general public, and to the Supreme Court, that the New York Times v. Sullivan test can be met in an appropriate case, so there is no need to change the test. A victory for Fox would provide support for the DeSantis theory that the law needs to be revised and ultimately strike a blow to liberal democracy in America.
My guess is that the attorneys for Fox will push desperately for settlement now that the company’s summary judgment motion has been denied. Let’s hope their client can’t be persuaded to make a deal.