Often the problem is the control and access plane for this disks and the tapes is vulnerable. Obviously, in the case of DAS this is far more problematic since the OS typically manages its disk's presentation.
I suspect the reality is that cryptolockers for tapes are coming slower because tape drivers and access are a bit exotic. If you had a driver or a backup program infiltrated for your tape library, you could potentially be writing crypolocked tape backups for months without realising. Often basic restore testing would determine that if it were the case. Also, the lack of random access on linear tape significantly limits attacks after the fact.
When I work with large enterprise NAS storage, often these devices are able to manage your storage and your snapshots in a way that is not directly accessible to operating systems aside from the NAS OS. This doesn't preclude malware attacking a vulnerability in the NAS OS in order to get access to that control plane to purge snaps via a remote code execution vulnerability or something, but like tape libraries, because there are a lot of vendors on the field there is a reasonably low chance a cryptolocker will know how to exploit your specific device.
To me, the big thing is speed, just as Mr. Newman rightly pointed out. However, where Mr. Newman talks about the signficantly longer RTO/RPO for tape, I focus more on the time to total data loss on disk based backups. I'm quite familiar with panicked calls from colleages saying "a cryptolocker has ripped through our primary datacentre backup disks and is now working on the second datacentres backup volumes". You see, in these scenarios, Mr. Newman's high speed disk RPO/RTO times start to extend out to infinity (or the time it takes to pay the ransom). If I have to programmatically turn on a switch to de-airgap my backup disks in order to run a backup, and in the time that the backup occurs, a crytolocker can eat all of the other existing backups on the disk system, then my airgap was useless.
An air-gapped disk system can be done, but that doesn't make the disks ideal for archiving. If I need to get someone to offsite my disks the way I get them to offsite my tapes, my data is almost guaranteed to be bad by the time I get be disk returned for a restore.
Cloud providers will be the next target. While I doubt cryptolockers will be able to encrypt virtual tapes and snapshots in the cloud, I suspect the low hanging fruit is still the control plane and accessing servers that either have access keys or profiles attached to them that have access to delete snaps, virtual tapes, so that once the OS is locked up, there are no further restore points.