Stars who have been typecast
Stars who have been pigeon-holed into one-note wonders.
Sticking to what you know can be a successful formula in the real world, but in Hollywood, getting typecast is a double-edged sword. Yes, it can help with maintaining a steady flow of work, but on the other hand, if you're typecast as a ditzy blonde, every day at the office is like Groundhog Day as you tire of hearing jokes that begin with, "What's the difference between a blonde and an [insert inanimate object]?"
It's unlikely that Reese Witherspoon's limited range is the reason she's never played the role of a cross-dressing mutant cyborg, but it may be that we, the audience, are to blame for not wanting to see her in anything other than "girl-meets-guy" stories. With that in mind, here are some more egregious examples of actors who always give the people what they want by repeatedly playing the same roles over, and over, and over again.