I agree with the ones below who say that it’s because of economy of scale, but I also think they made this choice because we’ll see more at the WWDC and in the next years. Apple keeps saying the iPad is a computer, when in fact it isn’t. But the iPad is capable of many things the Mac can’t do. It has the pencil, it can become more portable when used alone, it has 5G, cameras, the lidar and more. As long as they can sell both, they’ll keep doing it, but I think at some point 13” Macs (at least the Air and the cheapest Pro) will be replaced by the iPad, when it will have a better software. After the Apple Silicon announcement many choices started making sense, and in a similar way this iPad will be a way to test in which direction the computer market will take.