Cultivation of key opinion leaders before a new product is publicly announced is important because

journalists rely on opinion leaders to provide objective judgments about the quality of the product.

Explanation:

Opinion leaders are basically the influential members of a community such as experts, journalists, educators and celebrities who are held in very high esteem and are also said to have a more share of voice and media coverage than many other people.

They are the first set of people to test and adopt a technology service or product and then transmit the information or experience they have acquired to other members of the public. Journalists rely greatly on these people for them to provide objective judgments about the quality of the product or service.