It's probably cheaper to squish everything into one small PCB on one side of the machine.

Most people use a mouse on the right so having a wire where a mouse will be can be annoying.

Yeah, but most people will also be using Bluetooth pointing devices.

That's the point. You don't want to be running your bluetooth mouse into whatever you plugged in on the right side.

That might be the reason, but the number of people that actually use a mouse these days is tiny.

Maybe, but having wires coming out of the same side as the pointing device is annoying. For cost reasons you have to pick one side. So put it where it causes less issues.

Most people won’t be using a mouse with their MacBook.

So people like you spend more