They definitely do move markets. What you need to know is that they are buying short-dated call options. These options expire in less than 2 weeks, and are usually far out of the money. They require "dealer hedging" as the market makers providing these options do not want to be exposed to the massive amount of risk implied with the movement of price. The market makers are then required to buy massive amounts of the stock in order to hedge against any movement in the underlying stock, which can cause a "gamma squeeze" when market makers are unable to purchase enough of the underlying asset.