The mouse in the video he was using looks comfortable to use because it is big and round.
that's how they were back then.
It has more to do with limitations of technology at the time when they're new, as the first of anything usually starts off physically large, and as the technology advances, they're able to make it smaller.Computer keyboards and mouses did seem bigger back then, but keyboard, mouses, and computers were very expensive in the past, so making them bigger may make people feel like the mouse, keyboard, and computer was more worth it.
It has more to do with limitations of technology at the time when they're new, as the first of anything usually starts off physically large, and as the technology advances, they're able to make it smaller.