FYI, this is really asking the same as this other post even though it does not specifically mention ZGP (Zigbee Green Power) support:
https://community.home-assistant.io/t/wth-doesn-t-zha-support-friends-of-hue-buttons-yet/472645
You can submit a symbolic vote here to show interest for ZGP support in ZHA → https://community.home-assistant.io/t/wth-doesn-t-zha-support-friends-of-hue-buttons-yet/472645
But in the end, Home Assistant need more volunteering Python developer(s) with interest in low-level Zigbee support to look at existing ZGP code pull request and open a new code pull request for the zigpy library (ZHA dependency) or create new code that is acceptable for merger:
https://github.com/zigpy/zigpy/pull/656
PS: You might have many Zigbee Green Power (ZGP) devices, but statistically there are not many different ZGP devices on the market that are actually different products, (as most actually contain the same type of ZGP module made by EnOcean), however those available a relatively popular because of the “Friend of Hue” series as well as a few Philips Hue branded products that use the ZGP technology: