The hackers probably had a history of being reliable enough (in the cyber security world) to provide the encryption key upon payment.
Uber made a calculated decision to pay the $100k vs losing millions in a PR disaster.
Of course that would only work if word doesn't get out.
My 2 cents.
I hear this happens a lot to hospitals.
Doctors can't work on patients if they don't have access to patient records. So hospitals pay up.