To be more direct, one thing we lack is funding. AMD has provided RDNA 2 and RDNA 3 GPUs for the Debian CI, but to fill out the rest of the architecture matrix I have been personally buying GPUs. That's been sufficient for covering most architectures, but we will need a sponsor if we are to acquire CDNA 2 and CDNA 3 hardware.
Our goal is to cover every modern discrete AMD GPU architecture on the CI. At the moment, that would be Navi 33, Navi 32, Navi 31, Navi 24, Navi 23, Navi 22, Navi 21, Navi 14, Navi 12, Navi 10, Aldebaran, Arcturus, Vega 20, Vega 10, and (maybe) Polaris. I have been very successful at bringing the AMD GPU libraries to architectures that are not officially supported upstream. Unfortunately, I can't afford to keep buying systems out of my personal funds. I have personally spent ~7k USD on hardware for the CI and I have been offered reimbursement from the Debian project for my next ~5k USD in spending. That has given us a good foundation, but we could do more to improve hardware support if we had more funding available.
Please consider donating to the Debian Project [1] if you wish to support their efforts.