If you think about their intention at the beginning, they were not expecting the next trader to do anything, they were just executing their plan.
Activist Investors also don't care about the next trader actions. They are buying the stock for a strategic reason, i.e. to gain enough control to put them on the board of the company and effectively enforce the company management to change some or all of their actions. The ultimate goal of course is to make money, but they want to participate directly in creating the shareholders' value (And this might or might not be related to the stock price), sometimes activists want to force the company to start paying dividends (Because they have a pile of cash and they are not effectively using it), sometimes they want to force the company to merge with another, sometimes they want to enforce an acquisition or sale of some unuseful assets and distribute a one time special dividend form the proceeds of the assets, etc...