Why is ATM straddle price considered the “expected move” of the market?

I am a complete beginner in options and I am trying to understand one core concept. People often say that the ATM straddle price represents the “expected move” of the market. For example, if NIFTY is at 25000 and the ATM straddle is 200, people say that the market is “pricing in” a 200 point move. My confusion is: 1. Why does the straddle price represent the expected move at all? Who decided that this number corresponds to movement? 2. What does it really mean when we say “the market is pricing in a 200 point move”? Does the market actually expect it to move 200 points, or is it something else? 3. Why would someone pay 200 premium if they think the market might only move 50 or 80 points? I am not looking for strategies. I just want to understand the **core intuition behind option pricing, straddles, and the idea of “expected move”** in a simple conceptual way.