Copying music CD's was a grey area, but it's a grey area that you can do in a semi-legal capacity. There was no reason legally that Apple couldn't create a CD ripping process in iTunes. It's the user's responsibility to not use it illegally.
However, if CDs were encrypted, Apple would get in trouble if they broke that encryption to let you copy CDs to your iPad. You could find some more shady 3rd party tools that would work around it, but Apple's whole model is that it's easy to use and that it just works. Having to download an illegal 3rd party tool to rip your CDs and put them on your iPod isn't something they would do.
Similarly, iPods have had video playback for ages now, but there is no method to copy DVD video to your iPod through Apple's tools. You can pop in a CD and it asks you if you want to import it into your library. You pop in a DVD and it just asks if you want to play, no option to import. If they let you import it, they would be breaking laws. The brand is established, and was established by the simple copying of music, so it's not important that it can't copy video as easily. But if it couldn't copy music easily, would it have even been a thing?