Market makers warehouse options risk on behalf of the rest of the market. They are willing to do this because they hedge the directional component — delta — out of their book. When they sell a call, they buy a fraction of a share of the underlying. As the underlying moves, the call's delta changes, and the dealer must adjust the hedge to stay neutral.
That continuous adjustment is delta hedging. It is the channel through which options positioning becomes a mechanical force on the underlying price. Without dealer hedging, gamma exposure would be a number on a screen; with it, gamma exposure is a flow forecast.
Why it is mechanical, not optional
Dealers do not choose whether to hedge — their risk management and capital requirements compel it. This is the structural reason why GEX-based setups have edge that pattern-based technical analysis does not: the flow is forced, not discretionary, and forced flows are predictable.