We all saw Mount Sibo on Isla Nublar explode in Fallen Kingdom, killing countless dinosaurs in an absolutely heartbreaking scene.
There is also the fact that the Pterosaurs could have flown away to safety, to Costa Rica or perhaps Isla Sorna.
The site B island has basically been ignored in the Jurassic World series but the DPG website indicates there was a drop in population on Isla Sorna and the remaining animals were transported to Isla Nublar.
The very assumption that both island’s dinosaurs are completely extinct leaves room for a nasty surprise when some find a way to survive.