Google acts this way because they can. They are a popular SE from back when they were relatively honest and unbiased and they also buy traffic from Mozilla, iOS, Opera etc. They use that traffic to push down competitors and promote their services via Search completing the circle.

When they get some real competition they will be nicer to their users and consumers. If you want to advertise online in any meaningful way, you cannot ignore Google. They know that so they act as a monopolistic tyrant (also see At&T, Verizon, banks etc)