All phones have orphaned kernels. They are orphans because the source code to run the physical hardware is not available. The manufacturer adds these binaries in the last step of the ROM. They cannot be reverse engineered effectively and every model is different. Reverse engineering one does nothing for the next.
The hacked ROMs are maintained by people that know the kernel source at a crazy deep level. They know both the original kernel that the orphan is based on along with the state of every change and CVE that gets fixed in the current kernel. They are back porting all changes to the old kernel in order to keep it going. Eventually this becomes untenable or they lose interest.
Embarrassing country to live within, but Hitler talk and our genocidal crusaders state make us the evil of greater proportions now.