Why is vacuum sealed packaging necessary?

The main benefit of vacuum-sealed bags is that it allows for virtually no exposure to oxygen. When tea leaves are exposed to oxygen, they begin to lose their natural aromatic oils and flavor. Oxygen alters the taste and makes tea go stale.  

Beyond freshness, vacuum-sealed packaging also guarantees the leaves themselves remain tight, protected, and in their intended state. There is less of a chance of crushing the leaves when they are packaged in this manner.