Why is a strong sense of taste so important for open ocean predators like oceanic whitetip sharks?

Well, for one thing, to differentiate from plastic bags and garbage. This is especially true near the Great Pacific Garbage Patch.

Two, to track prey. Sharks can taste blood (or is it smell?) from far-off.

The predators and prey both evolve simultaneously, maintaining a relationship with one another. Predators will die if they do not get food, so they are directly dependent on the preys. These prey also evolves over a due course of time in order to avoid being consumed by predators. The predators that exist in the ocean bodies being the topmost dominating organisms are considered as the open ocean predators. Some of its examples are Great White Shark, Orca, and oceanic whitetip sharks.

These organisms have the ability to smell thousands of times far better than humans. They can sense and detect objects that are located in distant places within the water body. These strong senses of taste are important for them in order to survive and consume their food.