There's a very different risk profile for the buyers of class A shares vs. class C shares in the scenario above. The activist shareholder is trying to make the future happen; the passive shareholder is trying to predict which future will happen. The activist shareholder has a lot more information available to him, notably how close he is to winning control of the company. Some of that information may leak via the stock price and cause a run-up of class C shares, but a passive shareholder faces significantly higher risk when trying to assess the likelihood of activist shareholders winning a proxy battle, because they don't know how many shares the latter has.

It's much like how Porsche cornered the market in Volkswagon shares. Until the last couple hours, the market at large had no idea how close they were to a corner.

Also, remember that the price of a stock is set at the margin, but the value of one's holdings is an average. Imagine that an investor has amassed 100M shares of Google at an average price of $20. If they get to 100,001K, the value of Google will shoot up to $50. It is rational for them to pay any price up to $3M for those last 1000 shares, because their profit if they get them all is $3B, but if they are missing even one of them, they get nothing.

Same reason eminent domain laws exist: without them, it is rational for a large organization to pay any amount up to the total value of the project to the last few holdouts that are preventing it from being completed.