It's weird because the easier thing also seems like the obvious thing, and it's clearly better.
It's good for smaller screens. I was on a Zoom video conference last week, and all I could think about was how so many people who weren't allowed to/going to speak were taking up valuable screen real estate.
Then I see three boxes of the other people that are smaller than they would otherwise be if evenly divided. Most of the screen is black empty space.
Minimally I'd prefer a gallery view of all speakers option and it's probably the better option up to at least 6 people.
I think there's also a practical advantage of placing tiles haphazardly: it might help spatial memory. It's a lot harder to focus on or find a particular rectangle in a sea of rectangles than it is to follow a shape than looks a little different from the rest. However, I have never used FaceTime group calling (because I don't have most of my friends' phone numbers), so I don't whether this is effective in practice.
It seems like bad design to waste space on a small screen because it looks 'boring'.