Almalinux is used for desktop computers (along with RHEL and windows). This is about the control system computers, which have dedicated hardware for various tasks. It was planned for them to also use almalinux, but they dropped support for a bunch of old hardware architectures. This made Alma unsuitable as some of these custom computers just would not be supported. The cost/risk of redesigning just would not make sense. Hence: plan B, which is Debian and its many supported hardware architectures.