The microwave that came with my house

This is probably the reason why your popcorn button actually works. If your home already has a built-in microwave, it’s likely a higher quality one than what you could pick up from the hardware store. Most consumer-grade microwaves, regardless of the brand or model, are all identical, as they all use components sourced from one single manufacturer that makes one single version of them. The only thing that’s different is the plastic shell they put it all in and the logo they slap on the front, but the important things like the magnetron and control boards are all the exact same hardware.

But the microwaves that are usually built-into the home? Those are the good ones. Those are the ones where the builder spent some good money, because it was included in the design spec to begin with. Care went into the selection of that microwave. That microwave is more likely to have the moisture sensors needed to actually have functioning popcorn, reheat, and defrost settings that do more than just assume an appropriate time/power setting.

Having a proper microwave is a totally different experience. I had one at an old apartment of mine that was amazing. It had a button that just said “Reheat”, and required zero other inputs from me. I could put my food in, regardless of what kind of food it is or what quantity I was making, and press the Reheat button once, and it would bring it to the perfect temperature, hot all the way through. I wish I could’ve taken it with me when I moved out.