Why Do Classical Record Labels Overprice their Wares on the iTunes Store?

There’s one thing I don’t get about classical record labels and digital sales. Here’s an example: The Belcea Quartet’s complete Beethoven string quartets, on Zig-Zag Territoires, a French label.

On the iTunes Store:


And on Amazon.com:


What’s the logic behind that? This is just one example of many. To be fair, this is less common with single discs, but the prices of most box sets are much lower on plastic.