Why does the silicone mold didn't cure completely inside?

Because rtv2 liquid silicone rubber is a kind of condensation curing silicone rubber, which is cured by absorbing moisture from the air. In order to provide a significant shelf-life for the silicone rubber, we will dry out the water in the silicon rubber. 

Solution: Add 0.1% water into the silicon rubber and Stir over a low speed briefly when you use it.