This is not the only sector working like that, you must be able to move to opportunities or new propositions, many people from big companies just quit and made their own studio or move to opportunities more interesting and involving. Also the more intresting jobs are not always on the bigger studios; for example Torchlight 1&2 was made by a small indie studio composed of people coming from Blizzard that worked on Diablo, and there is many others examples like that.