That part is to stop them from choosing the decryption key after sharing the encrypted strings with the intended result of guiding the outcome of the hash. If t

That part is to stop them from choosing the decryption key after sharing the encrypted strings with the intended result of guiding the outcome of the hash. If the content of the strings was wholly random a participant would be able to claim that the gibberish resulting from using a key chosen later was what they had meant to encrypt in step one.