> If you have to make a new copy from the original reels, what if someone is hoarding them?

This is a legitimate problem in public domain releasing. If you're trying to release a really good public domain version then you might need access to very high quality source materials. With a movie it would obviously be nice to scan the camera negatives. If the studio has those negatives in a vault, then you're cooked.

Didn't Bill Gates or some others buy up thousands of old artworks and put them on ice so they could paywall the scans?