Dolphin died March 2022, then the publisher received the manuscript in June 2023. Then review took until 10 April 2024.

More generally, they weren't doing this in response to the recent outbreak, it was sort of a coincidence that the disease gained media attention at the same time of this paper's publication. Academic researchers are expected to publish around 2 papers a year, and each paper tends to take a couple years.

tl;dr: it's an academic study, not the dolphin CDC. blame the publishers and universities, not the researchers.