Mainframe tape is a funny thing. Or at least it can look funny to a person that doesn't work with mainframes.
Funny because mainframe tape does a bunch of things. In the open systems world, life is simple by comparison. Tape does (or did!) basically one thing: backup. Yes, you could argue that it was used for archiving too, but that argument largely depends on the notion that backup and archive tend to be the same thing for open systems folks. Which isn't necessarily a good thing, but it is certainly the case more often than not.
In the mainframe world however, tape does at least four things: backup, archive, batch processing, and migration (for DFHSM). Now some of these, it could be argued, are sort of suited to tape. And some are not. In fact, as time has moved on, the value of tape to each of these has degraded.
And as innovation has occurred, that value has degraded even further. Because mainframe tape is very much like open system tape in one key respect: it isn't very much fun. It is unreliable (relative to other IT systems), it is insecure, it is slow, and it is an operational nightmare. And on top of it all, it makes disaster recovery planning, testing, and execution really really difficult.