For the same reason a storage company shouldn't be able to burn all the stuff in your unit if they evict you.
1. That's arson, a crime.
2. I have a contract with them (including consideration) to store my stuff.
YouTube doesn't charge rent or other fees, and I'm not sure how they'd auction your digital copyrighted IP anyhow.
Youtube could do something similar, by providing you 30 days to download your content.
instituting a 30-day retention period to exporting content would be really good for users. shame we can't pass tech laws in the US.