According to wiki
Director Colin Trevorrow has stated that the Indominus rex, the synthetic hybrid dinosaur at the center of the film's story, is symbolic of consumer and corporate excess. Trevorrow stated that the dinosaur was "meant to embody [humanity's] worst tendencies. We're surrounded by wonder and yet we want more, and we want it bigger, faster, louder, better. And in the world of the movie, the animal is designed based on a series of corporate focus groups."
He also stated that "There's something in the film about our greed and our desire for profit. The Indominus Rex, to me, is very much that desire, that need to be satisfied."
Not that we have to take his word for it!
We can let it 'symbolise' whatever we want - referencing why from stuff within the film - or not!
It might also symbolise or represent a whole load of other things.
And we can also ask, why a dinosaur? Why do dinosaurs have traction as symbols today?
(I don't have a clever answer for that question!)