The one thing I don't really get is why, pi's everywhere? Most of the times an esp32 will be more than enough for a few sensors. No need to be running a full OS and the added benefit they are actually available right now to buy.
- Hydrogen fuel cells are a better technology than batteries - Zigbee is a better wireless protocol than wifi - you dont need a RPi, an ATTiny and some transistors would work fine
sure, but wifi is being improved for tons of use cases and Zigbee only really has the one use case just now, getting started writing code for x86 with a full OS is much simpler than for a microcontroller etc etc
ultimately the network effect / whatever kick in and the popular stuff usually ends up winning IMHO