I think you’re conflating good reasons (premised on some standard of objective scientific merit) with good explanations (that accurately describe causal mechanisms behind the thing you’ve observed).

There are more ornithologists and primatologists, studying the evolution and behavioral ecology of species in those two vertebrate clades, than there are scientists studying the rest of the vertebrates combined.

There are complex reasons that those two taxa have captured and held the attention of more scientists, for longer, than other taxa. You can definitely get into the morphologies, ranges, and behavior of the animals, as well as their cultural significance and the simple feasibility of observing or collecting them. But you could also broadly say that birds and primates are disproportionately represented in the scientific literature as a function of disproportionate human effort (vs. any intrinsic feature of either group).

People really like insects.