14 years was good enough in 1710, when it was prohibitively expensive to publish anything and global distribution was effectively impossible. Today, those things are basically free and happen at close to the speed of light. If you can't make money off of something over 10 years, you fucked up. 10 years might even be too long.

It's 100% fine if disney wants to wait a decade to make a movie about something. After that 10 years so can everybody else! There's no amount of time disney can't hold out for anyway. What matters is that artistic works get into the hands of the public faster, not how much money an author might lose out on in licensing deals. Copyright doesn't exist to protect possible film deals for authors. It exists to promote the creation of new works. If disney waits 10 years and makes their film then without a license fee, mission accomplished. That's a new creative work. They can then compete with every one else making new works based on that property.