I don't follow - are you referring to this specific malware (which tbh I don't know much about) or ransomware in general? There have been plenty of ransomware cracks and decryptors released - programmers aren't perfect.
Oh, just ransomware in general. I was under the impression that most of the big ones just did simple encryption, and hold the decryption key ransom on an external server. It would defeat the purpose if they kept the decryption key on the local machine, because yeah, then you could just release a tool like the ones you mentioned.