Prove it..
I am honestly baffled why this is even really a question. Why did they pull 20 pages of rules from the DMG? Because not enough people used them. Why did they add 40 pages of planar stuff? Because people are using that material. It's not rocket science.
You can't, because you assume the decisions being made are based on some metric as opposed to just being made because.
Let me ask you this: why does every alt 5E include those rules if "no one used them"?