The kernel driver for HDCP is about orchestrating it to happen on the GPU, not about implementing HDCP in software running on the CPU. I.e. the place you need to hack is in the GPU so it continues like HDCP is enabled even though it isn't, not the kernel driver asking the GPU to enable/disable HDCP normally.
Meanwhile, kernel level anti cheats live their full life on the CPU and the logic is itself the software driver. Hacking the software driver therefore gives you actual direct control of the anticheat behavior and functionality itself.