Technichally, Isla Sorna was more of a "testing grounds" sort of thing.
The dinosaurs created on that island were prototypes, to make sure the DNA shit they were doing worked, and that they actually stayed alive during a normal lifecycle. Which is why there are dinosaurs found on Sorna that weren't on Nublar; They either weren't ready, or were too new in comparison to the event of the first movie to have been added to the park.