On purpose.
If Styram were to develop the app for Athom, wouldn’t Athom be listed as the app developer? 
The code is still “Public”. If you click “Report an issue” in the Homey App Store, you’ll be redirected to the corresponding page on GitHub → GitHub - StyraHem/Homey.Sonoff.Zigbee: Sonoff Zigbee Devices · GitHub
According to Abe, there are already plans to develop a new Sonoff app based on the “official” Sonoff app by Styrem. This has already been discussed in the following thread → Sonoff SNZB-01P appearing as a battery in Homey Pro 2023 - #17 by macmonty
