Because animals only dream about what they know, that's why they're called animal dreams. Like this quote:



Codi: "So you think we all just have animal dreams. We can't think of anything to dream except our ordinary lives."
Loyd: "Only if you have an ordinary life. If you want sweet dreams, you've got to live a sweet life."
~Barbara Kingsolver, Animal Dreams



While people will always have animal dreams technically, this will prevent you from having really boring ones. You'll be able to have dreams that will be worthy of asking people to interpret it in the interpretation forum.