To be frank, the ransom payment is a typical prisoner dilemma. If nobody get the file decrypted (some company will have some security assessment and info sharing policy with authority), it will destroyed ransomware attacker reputation thus destroyed the future "prospect". However, there is chances that ransomwware attacker make blunders.
The issue lies on the encryption key. To maximise the ransom profit, generate a new crypto key every PC is the way to go. However, it will also introduce risk of the crypto key missing in the transition to the bad guys C&C (command and control) server.
So having pre-generate crypto key will guarantee a decryption, but it also means those who pay may "reuse" the decrypt key in many PC.
As suggested by @Josef, the attacker may use an asymmetric key to encrypt am adhoc unique key. I.e. Ransomeware code use a public key to encrypt the adhoc crypto key. This mean either the malware need to send this first level encrypt data back to C&C server. But there is one catch for this mechanism : If the authority block the IP of the C&C, it will "hurts" the syndicate "sales performance"(sarcasm).