Apple doesn’t make their own thermostat, and while the ecobee Smart Thermostat does now include Siri it’s not because Apple put it there. Announced at WWDC 2021 was the ability for third party device makers to integrate Siri into their devices. This comes with some limitations around personal data as Apple doesn’t want any potential abuse of that by third parties, but many common Siri functions commands and queries can be used.