Remember when she was the heir apparent to Natalie Portman? Then whoosh, she just sorta vanished. Was it the Pirate movies that did her in?
shareThe answer is in your own question. It's not that she was the heir apparent to Natalie Portman but interchangeable. To make matters worse, she was also more or less interchangeable with Kate Winslet, too, who also kind of faded from status. That's what happens when you have two or more actors that are more or less cut from the same cloth. The less memorable one winds up fading into the background. (See Marilyn Monroe and Jayne Mansfield, Bruce Willis and Mickey Rourke, Gale Gordon and Frank Nelson).
shareI'll have to challenge you on that Bruce Willis/Mickey Rourke example. Rourke is by far the better actor, has more memorable performances, and (was) much better looking than Willis in every way during the 80s and early 90s. I still think fondly on a lot of Rourke's earlier work before he went topsy turvy sometime in the early-to-mid 1990s.
I think Rourke was his biggest enemy rather than not being memorable enough, plus Willis had Die Hard to keep him mainstream.