I'm going to say the answer to why they would spend so much time on side characters is that they love ice skaters more than they love ice skating.
I kind of feel like it's the opposite. They spend so much time on showing every single performance that it hurts how much time they can spend fleshing out the characters. One of the issues I have with the show is how one note so many of the ice skaters are. Besides Yuri and Yurio there isn't much characterization to the final six. They seemingly all have their gimmick/trait but they don't come across as real people.
However I do see your point but that's also why I feel the direction is undisciplined as the staff want their cake and want to eat it too. They don't have enough runtime for what they want to do so they're trying to do both with middling success in both areas.