Products with uncertain demand will most likely be produced at a lower volume to products with a certain demand and therefore sourcing from local manufacturers provides zara the speed it needs to test and deliver these products before they become obsolete and have to be sold at a discount. It is part of a responsive pull strategy.
Predictable demand products are made in Asia due to low labour costs and high volume of products needed. It is more cost effective to manufacture in bulk due to the fact that predictable demand products have a larger window with which to deliver products without becoming obsolete. It also means that they can be made before the season starts as part of a push strategy