My reasons:
1. Because I have them.
2. Because I like the content on them.
3. Because I like the way they sound on my SACD player.
I think those reasons should be sufficient. Need another?
4. Because I dread the alternative. After some 30 years of software engineering and system administration, I hate working on computer problems, and mostly won't, unless paid or desperate. Sure I've ripped CDs - I have many on my laptop. I have even more on a now-nearly-bricked Windows 7 machine. I despise forced obsolescence, and hate software that requires fiddling, maintenance, or perpetual updating or replacement. I want software to just work, the way an old-fashioned Bell telephone used to. Or a CD player, for that matter. There are threads here on AK that go on for months, trying to solve folks' computer-audio issues. Not for me. I'm not yet desperate.
I assert that the only way to know that a backup is good is to restore it.