Why market maker hedging moves price

The market maker has no view on market direction. They sell the option, then neutralize their directional risk by buying or selling the underlying, here ES futures or a basket of S&P 500 stocks. Gamma measures how much that hedge must be adjusted when price moves. So gamma is what generates mechanical flows, with no opinion behind them, and those flows print in your book as buying or selling that seems to come from nowhere. Understanding their direction is understanding why a level brakes or accelerates.