IIRC the modus operandi for at least a few of these large ransomware attacks was that the initial attackers who succeed in phishing or whatever would install a remote backdoor there and sell the access for something like $2-10k to professional teams who have the infrastructure and capacity to handle it "properly" - use that foothold to spread across all the workstations, gain user credentials to access servers and destroy backups, and then trigger ransomware everywhere at once perhaps a week after the initial infection, transforming it from a driveby nuisance to a targeted attack that's hard to recover from and that can justify a big payout. Some of the victims had reasonable backups, but they were intended for disaster recovery, not malicious action; so they were accessible from the compromised machines and thus could be disabled or destroyed.

An automated attack that manages to hit a random workstation can extract a ransom of a couple hundred dollars; but if they invest a couple day's hacker labor to move deeper, then there are many public cases of $50 000 - $500 000 ransoms paid, and multiple cases such as Baltimore city and Atlanta city which suffered losses in excess of $10m as a result of not paying the ransoms.