No reason, few decades ago oven used to work just as well as they do today with knobs, thermostats and spring timers.

That’s why I said good question.

The oven I mentioned isn’t this smart but there exist ovens like

COOKING MADE SMARTER WITH WIFI POWERED BY SMART HQ: Voice-enabled cooking allows you to turn microwave on and off, add time or change power level via Alexa or Google Assistant; Scan-To-Cook Technology saves time and optimizes frozen food preparation