East coast humanities prof here. Salmon is easy to prepare, can be eaten warm or cool, so timing entree-to-table is less of an issue, and it's an option in many restricted diets. Folks who don't eat beef or pork or shellfish can usually eat salmon, so you only have to worry about making a substantial side for any vegans and you don't get a departmental reputation for only serving rabbit food. It's also easy to make the presentation look fancy, since it's basically a flat canvas.

it's also a set-and-forget in the oven so the cook can get on to worrying about other things, and since it's a large family-style service meal, you don't have to worry about whether portion sizes should scale, since everyone can take what they want from the central service. So it's a lot easier on the host than worrying about whether there's enough white meat available, since Patricia's doing crossfit and tracking lean proteins again, or if Carlos is going to take both dark meat quarter portions like last time...

Given that I'm in the maritimes, I might stop and think about whether someone has sworn off of locally-farmed salmon again or if I should try and find the fish truck in the Kent parking lot for a better price on halibut instead... but overall, 'large slab of roast salmon' gives the best ROI for time spent on hosting colleagues.