Well, the answer is that because these products are very proprietary, migrating from one backup software to another is rarely a simple task. Certainly, backup software will have general restore capabilities that can enable you to copy your tape data to a server. However, this does not always work. Switching to another backup software is something almost no products support.
Remember that this is not always an easy task, and can be time consuming for your IT staff, often with very little return. Consider contacting us or another backup tape migration expert if you are serious about changing backup software applications.