And the PCB is compact because there are tons of high-speed and/or noise-sensitive signals that need to be carefully routed. If you make components modular you

And the PCB is compact because there are tons of high-speed and/or noise-sensitive signals that need to be carefully routed. If you make components modular you now need to run them over (typically fewer conductor) buses. The buses will be slower than direct hardware connections and now when you want to upgrade your 1080p camera to 4k you're still limited by the bus speed of the base phone.