The Jurassic Period, approximately 201 to 145 million years ago, was a time when dinosaurs ruled the earth. If you were a billionaire opening an amusement park with living dinosaur attractions, you could do worse than to name your place "Jurassic Park." The name sounds appropriately exotic, and it's still easy to pronounce.
As the novel focuses on the suppressed story of the park's rise and fall, it is appropriately named after its subject matter. The book is arguably more setting-driven than plot-driven—and the setting certainly matters more than the characters.
Nitpickers point out that Jurassic Park has dinosaurs that didn't live during the Jurassic Period. The Tyrannosaurus and the Velociraptor, the most famous denizens of the park, lived much later, during the Cretaceous Period.
This is true, but let's be honest, Prehistoric Park or Dinosaur Park or even Cretaceous Park just don't have the same ring to them. Sometimes you've got to sacrifice precision for marketable aesthetics.