Why can't I download Windows 8 Pro with my MSDN subscription?

The "VL" in "Windows 8 Pro VL" means "Volume Licensing." It is only available for Volume Licensing customers only. Which you probably aren't, if you're reading this.

Windows 8 Pro is actually bundled within Windows 8, the only difference being that you need to use a different key.

This information is hidden within the Details of the "Windows 8 Pro VL" list item. The details of the Windows 8 list item only hints at this fact, saying

This file contains multiple products. Please refer to your product keys to determine which products are included with your subscription.

In order to download and install Windows 8 Pro with your MSDN subscription:

1. Log into MSDN and click the Downloads link
2. Click the link for Windows 8, or view the complete list and search for Windows 8
3. Click the download link for whichever flavor of Windows 8 you prefer (x86, x64, N or Not)
4. As it downloads, click the "Product Keys" button
5. Click the "Get a Key" button for Windows 8 Pro

The Windows 8 download will allow for both standard and Pro. The version will be determined by the product key you enter.