Because it's assumed that you would have done the backup when you imported to the first catalogue, which is more efficient and effective. Import from Catalog has other roles - eg moving work between computers.
John
That's exactly what I wanted to do - copy work from one computer to another.
Let me throw a different operational model at you.
I'm away from a week, shooting and photos go to two places: the laptop internal hard drive and an external drive which serves as my backup. I return home and the task is to get the data from the "roaming computer" to the "main computer." What I should be able to do then is connect the external drive that I had connected to my laptop to the "main computer" and import from that with that import also copying files in from the external drive to both my desktop and the real backup.
In this instance, the external drive serves as a temporary backup for the laptop and also the means for transporting files from the laptop to my desktop. Both the laptop hard drive and external hard drive that I connect to it are somewhat smaller than my backup but they're big enough for a week's shooting.
The other piece to this is that I need to get a copy of the catalog on to the external disk.
The other method here is to do all of your initial imports, when using a laptop, onto an external disk (where the initial catalog data lives) and have the backup copies live on the laptop. Then there's no special action required to get the catalog onto the external disk.
I can do all of this manually (copy from the external drive to the internal, then copy the trip catalog) but that isn't really as user friendly as it could be.
If you only have one computer and only ever work from that one computer, then this does not apply.
It just dawned on me that you're probably expected to do an "Export" before doing an "Import" in scenarios like this. But why should I need to? If the photos and catalog are already on an external disk, why do I need to write it all out to a new copy with export?