How come mold keeps coming back?

Perfect conditions. Sounds nice right? You want to plant tomatoes and you wait for the perfect conditions. You want to go to the beach, you wait for the perfect conditions. 
Flowers bloom and birds make nexts. Perfect conditions.
What you don't think about is how perfect conditions also means something so disruptive is happening right under your nose. Water travels, this we know. What we think we know is that mold needs warmth to grow. It doesn't.  Usually, mold enjoys the same temperatures that we do.
Extreme heat doesn't kill mold and neither does freezing temperatures. These things both do the same thing, it keeps mold waiting. It sits and waits for the perfect conditions to spread and grow causing destruction in its path.