Why does Disney have such a hard-on for keeping Mickey's Choo-Choo?

Since Mickey's Choo-Choo and 11 other shorts went into public domain today, I decided to upload the short onto YouTube for anybody to see. Unfortunately, Disney struck it down even though it's in public domain. The thing is, even before these shorts went into the public domain, all of them were on YouTube with complete synchronized sound except for Mickey's Choo-Choo. Why is that?