Things don't have to be connected directly to the Internet to be compromised by Ransomware. There are sooo many vectors into an organization these days; email, direct messaging, exposed systems, un-patched systems, personal devices, removable media.
To the points made above about backups - yes, that's the one method of recovery available right now that doesn't involve paying the bad guys. But it's still expensive.
In order to make SURE you have eradicated the bad guys from your systems, you have to either have familiarity with the exploit used, or you have to rebuild EVERY system from a known good base. It's a harsh reality. Unfortunately, most people pay the bad guys to unlock their systems, then have to do all of the work anyway to make sure they are out anyway.
To the points made above about backups - yes, that's the one method of recovery available right now that doesn't involve paying the bad guys. But it's still expensive.
In order to make SURE you have eradicated the bad guys from your systems, you have to either have familiarity with the exploit used, or you have to rebuild EVERY system from a known good base. It's a harsh reality. Unfortunately, most people pay the bad guys to unlock their systems, then have to do all of the work anyway to make sure they are out anyway.