I totally get where you're coming from. It would be so convenient if the Nest Thermostat could automatically use the average temperature from your sensors. Unfortunately, Nest Thermostats typically require manual selection of the preferred sensor for temperature control.
If you have specific sensors that you trust to represent the overall temperature of your home accurately, consider placing them strategically or in central locations to get a more balanced reading. In line with this, I also want to encourage you to use the feature of the Google Home app where you can send us feedback.
Fingers crossed for future updates that make this process even more seamless!