The reason they are usually found not to be takings is twofold.
First, they only prevent a specific type of relief. In most of them, nothing in them stops the landlord from suing for money damages, or even necessarily for breach of contract with ejection as a remedy. They only usually prevent you from filing eviction petitions.
Second, they generally do not state that you are not owed the money, only that you may not temporarily collect it.
See, e.g., https://www.inversecondemnation.com/files/eviction-moratoriu... (massachusetts)
(A federal court also declined to block it)
I am too lazy to look at all of them.
The reason they are usually found not to be takings is twofold.
First, they only prevent a specific type of relief. In most of them, nothing in them stops the landlord from suing for money damages, or even necessarily for breach of contract with ejection as a remedy. They only usually prevent you from filing eviction petitions.
Second, they generally do not state that you are not owed the money, only that you may not temporarily collect it.
https://www.law.cornell.edu/wex/takings goes through most of the current tests, and most moratorium rules fail them.
For example, taking again the MA one:
1. It does not allow permanent physical occupation (they are temporary)
2. It does not cause loss of all beneficial/productive uses of the land (you are still owed the money, and in fact can sue for money damages)
etc