Here's why:
* Tongue Position: The tongue moves towards the front of your mouth, almost touching the roof of your mouth behind your front teeth. This creates a narrow passage for air to escape.
* Jaw Movement: To accommodate this tongue position, the jaw drops a little and moves slightly forward. This creates a larger space in the oral cavity, allowing for a longer, more sustained sound.
Think of the difference between saying "bit" (short "i") and "bite" (long "i"). You'll notice a slight difference in jaw position and how the sound feels in your mouth.
It's a subtle movement, but it's essential for creating the correct articulation of the long "i" sound.