FarmVille - Why can't I upgrade my Zen Garden House to a 3-star building?

Update as of April 8, 2016, 10:00 am PDT

Good news Farmers!

The Zen Garden  House  can now be  fully  upgraded without having to unlock the other regions!

You may now enjoy  upgrading the building!

----------------------

Unlike the usual crafting building, the Zen Garden House has a maximum available upgrade for each region in the Story of Sakura. Players can upgrade it up to 2 stars for the first two regions - Plateau of Patience and Rivers of Balance. The 3-star building will be available once the Mountain of Strength region is unlocked, and it can be fully upgraded to 5-star in the last region which is Zen Valley.