Last month Apple released the OS for HomePod with an update. Although the users will not find any new features with the update, there is still a significant change in the code, says gto9to5mac which analyzed the latest HomePod firmware. The HomePod is now based on tvOS instead of iOS.
The software that runs HomePods, Apple tvOS and watchOS are all variants of iOS wit slight changes in the code according to the device and the interface. Unlike before the HomePod which was based on the software sued for iPad and iPhone, it is now based on tvOS.
It is important to note that iOS runs the devices which use the battery to power and run. It means the code that iOS has is different from tvOS which is always plugged in.
It now means that Apple will have less to code and also not to worry about that aspect because HomePod is always plugged in for power and does not rely on the battery.
Also, there might be another reason Apple using the tvOS for the HomePod now instead of iOS. That reason is that the iOS will soon drop the support for the A8 Chips. And as we know, the HomePods rely on the A8 chips. It can be another reason that Apple is shifting its OS to run the HomePods.