Every major discipline such as ethology, ecology, paleontology, systematics, development, genetics, population genetics, biochemistry, and molecular biology has a separate history that is contemporaneous with the theory of evolution. Model species such as Drosophila were chosen during the early twentieth century because they were easy to culture in the laboratory or because their chromosomes were easy to stain and observe under the microscope. The most pressing questions were often mechanistic in nature, pushing Tinbergen’s other three questions into the background. Who needs to know the nuances of the ecology of Drosophila when you’re trying to work out the basic mechanisms of recombination, the transcription of genes into proteins, and the like?
As mechanistic knowledge increases, then the need to bring in the other questions becomes increasingly important, but integration can require decades and is impeded by a variety of intellectual and sociological factors. If I were to nominate the single most important priority for the biological sciences, it would be to get everyone on the same page with respect to Tinbergen’s four questions.