This is not true, the panthor driver (previously pancsf) for mesa is actively being developed and funded, and already works quite well (I had a demo desktop running on prototye MNT Reform Next laptop at 37c3).
And the main panfrost developer Alyssa Rosenzweig has moved on, so the pace of development has declined significantly. At this point the Raspberry Pi 5 is more than capable and the Rock 5 has lost the primary advantage it once had.
It's nothing to do with that really. It's much more to do with the gen10 (Gxxx) Mali requiring a completely new kernel driver. Given that nouveau and other drivers required the same thing, this ended up being a long diversion into a lot of new common DRM infrastructure to make things easier for the next drivers who need to do the same thing. By comparison, enabling gen9 in the kernel was more like adding a couple of device IDs. See bbrezillon & dakr's talk here for more details: https://indico.freedesktop.org/event/4/contributions/181/