It's this. It's also one of the most profitable forms of insurance for the insurance companies since everyone needs it but few end up using it, and the fact that insurance exists at all drives the prices way up (like every other industry they touch).

On the other hand, once people started paying, the ransomware scene became an actual industry. Before, the "send money to this number to get your files back" part was a bonus scam and you'd almost never get a response, so getting ransomed was a death sentence for a business that didn't have working backups. Now the encryption key is sent 99% of the time the ransom is paid, and larger groups even offer tech support to their victims if they have trouble decrypting.

Source: half-remembered snippets from last year's CompTIA Network Security course. Can't actually double check it since we live in a capitalist hellscape where information is rented and goes poof after a few months.