Quoted from SpookyLuke:
I'll have to ask! I think there is a technical reason for that. I want to say that's the shape it was originally displayed but I will have to check with the smarter than me people.
Thanks for the reply. I understand the challenge of adapting the 4:3 original ratio to the wider screen on the pin, but putting it in a window makes the already small video even smaller. Using the whole 4:3 source video and just cropping off about 5% from the top and bottom, you can fill the screen with it and leave room for scores and whatever else on the sides. It'd give much better visibility without all the wasted, unproductive space that's there now.
Here's the current display (left) next to a rough mockup (ignore the hand, I just cut the shape the 4:3 video would occupy, and ultraman's hand was over the video) of what I'm talking about with the 4:3 source at slightly oversize with about 5% cropped off the top/bottom. This would be a much better visual experience, actually highlighting the integrated footage from the show.