We can only accept finished artwork that's within the standard spec of the CD industry. In the past, pressing a CD meant a big-time expense because you had to press 100s at a time. Respectability in the music industry almost requires you to submit a finished CD for consideration. They like the fact that it represents a finished retail-ready product. A product that may only need pressing and mass distribution.
Filmmakers are another group whose preference lies in CDs.
Some depend on it. Again, access to the material is quicker, easier, and more stable than anything else. It's less apt to get lost or damaged. And, with the right media, can last well over 100 years without deteriorating. Last but not least, a CD product gives independent artists a way of selling their material directly to their audience.