Why do they do that?

So then why does the button even exist?

just use it anyway

exactly, do your own thing

food theory:

I pressed the wrong button

Me who never reads the instruction, putting the popcorn and presses the button.

Very good point

I still use the button

I still use it and nothing's exploded so were good

There is actually a good explanation for this: popcorn packs are best when cooked at a certain temperature, and different microwave models have different temperatures.

:0)