Most likely because an engineer designs it, or it's designed by committee. Let's see, how can we sell this same microwave that cost us $30 to make, for twice the money? Oh let's add "features" such as a 'popcorn button' that makes popcorn, or a 'defrost tbone steak' that perfectly defrosts...

etc etc, That said, the inverter technology in the panasonics are worth paying for... not to mention that they do have tactile buttons and a knob... http://www.cnet.com/pictures/panasonics-nn-sd997s-microwave-...

I think the answer has to do with the illusion that more buttons = more features = higher quality = better.

I'd guess that each button equates to a feature. So nobody wants to be seen "removing features" from the product.

Microwave A:

- heats food for the duration you want and power level you want

Microwave B:

- heats food for the duration you want and power level you want

- thaws food

- warms pizza

- makes popcorn

- boils water in a cup

- etc.