This is exactly why they celebrate it as well. The pointless sacrifice at the other end of the world made them realize they weren’t British any more. It’s usually considered as a beginning of separate Australian and NZ national identity (political independence took some decades more)
Religion is useful for one thing and one thing only - as a barrier to depression. Having a predefined higher purpose neutralizes the existential dread, it helps you function in the face of a meaningless life.
Unfortunately it’s all false. Once you understand the the falsehood it doesn’t help any more. Which is why so many religious people cling to their religion. Giving up on whatever belief kept them alive equals suicide, and they want to keep on living.