2015’s Jurassic World also earned a PG-13 rating for ‘intense sequences of science-fiction violence and peril’, and given the story of this movie and that it’s set in the same franchise, it makes sense that Fallen Kingdom would get the same rating and reasoning.
Intensity and peril is the bread and butter of the Jurassic franchise.
And with the nightmarish Indoraptor, just about everyone looks to be in very serious peril.
The emphasis on violence also indicates that plenty of people will find out exactly what happens when nature bites back and suffer grisly deaths as a consequence.