Why don't businesses (or systems) seed their drives with files with known text / content and then use those files to reverse the method used to encrypt? It seems like having an adversary encrypt a set of known "canary" files should provide information to reverse the encryption?
Again, there may be a good reason (or many many good reasons) why this would not be a good solution, especially since I'd expect most OS installations have enough standard files to do this if it worked, but I am curious if someone knows.
Edit: From the helpful comments, this is a known class of attack on a cryptosystem called a plaintext attack. Using that information, I looked into how ransomware systems address this attack, and several, apparently, use per-file keys as, in part, a defense against this type of attack.