They do, but there are many other biologists who do too. What is odd is that those other biologists are often happy to do statistical tests on their observations. If Popper were correct, they wouldn’t need to.
Even the members of the Hennig Society, at the peak of their fervor for hypothetico-deductive reasoning, didn’t take a single refutation as decisive – they counted refutations of different possible cladograms and chose the “least-refuted” one. Which isn’t Popper’s approach to refutation.