[worik]

The plug between the cord and the device must be sturdy and meet regulatory standards

So it is expensive

It is cheaper to just attach the cord

That is the reason

[socalgal2]

plenty of devices have separatable cords. My rice cooker has a PC style plug. My water kettle has a magnetic plug.

[sowbug]

Some of that is because they want a single factory assembly line to produce one device that works in many locales. They build the rice cooker with the universal socket, then ship the right kind of cord when they package the product for a specific locale.