I've been in security for ages, ransomware was there but has evolved since then.
Two other reasons can explain the increase in ransomware, that merely correlate with the rise of cryptocurrencies:
1) The innovation of encrypting files hadn't occurred to ransomware operators yet.
2) The value of computer systems, and data, itself increased. Massively increasing the likelihood of victims paying the ransom.
Before crypto currencies 'FBI scareware', which held your computer ransom by disabling your standard UI, simply asked you fork over the cash via Western Union.
This increases the friction for consumers, but if the colonial pipeline was ransomed in the same way, and the ransom only payable over WU, then they would have done that instead.