As far as I understand, Music CDs are nothing more than some metadata along with a bunch of WAV files. So why doesn't Windows (by default) allow one to copy WAV files from a CD?
Audio CDs don't have any files at all. The tracks' data is compatible with WAV format, but their appearance as files is faked by Explorer and the Windows' CDFSs driver. (Some CD formats even have a data track alongside audio tracks, in which case Explorer doesn't show the audio tracks at all.)
Although I remember Windows 98 actually had a third-party replacement driver which added this exact feature, by taking the emulation further, and presenting .wav files with correct headers added. So it was fairly straightforward to implement, although I'd say more confusing UI-wise.
In the end, that's likely a decision that only Microsoft can explain, although "make it less straightforward to copy music as per RIAA's wishes" might be a good guess.
They are not WAV files with metadata, it is one continuous "file".
See this article about detailed explanation.
From the link:
If you view the contents of a music CD from Windows, you'll see that it contains a number of .CDA files each corresponding to a song track. (CDA stands for Compact Disk Audio)
I regularly get letters from subscribers asking why can't they just copy these files to their PC rather than first having to rip them to .WAV, MP3 or other music files.
It's a good question with a simple answer: there are no .CDA files on a CD. In fact, from a Windows perspective, there are no "files" at all.
A music CD differs greatly from your hard drive or floppy disk drive in the way information is stored.
Hard drives and floppy disks store data in concentric rings called tracks. In contrast, music CDs store data in a continuous spiral starting from the inside of the CD and ending at the outer edge of the CD. Kind of like a vinyl LP in reverse.
The format of the data stored on CDs is also quite different; it's a continuous stream of raw digital data rather than a collection of individual files.
The reason the data is stored in this strange way is the music CD format was developed in the late 1970s long before the age of the home computer. CDs were designed to be played by CD players and at that time nobody even considered that one day they would be played on a computer.
So what are .CDA files that you see on a music CD when you place a CD in your computer's CD tray?
These files are created by the Windows CD driver. They are simply representations of the CD audio tracks and are not actually on the CD.
Each .CDA file is a kind of a pointer to the location of a specific track on the CD and contains no musical information. CDA files are all 44 bytes in length and each contain track times plus a special Windows shortcut that allows users to access the specific audio tracks.
So if .CDA files contain no musical information, what happens if you "copy" a .CDA from an audio CD to your hard drive and then double click it?
If the CD is still in the drive then the corresponding track will play from the CD. If you remove the CD you will get an error message. That's because the .CDA file contain no music, it only points to where the music is located on the CD.
To work with music tracks on your CD you need first to convert them to .WAV, .MP3 or another file format that computers understand. That's what a CD ripper does and that's why you must use a ripper before you can work with your music files on a computer. Simple as that.