SWTOR is a big earner for BioWare and Electronic Arts. The extreme popularity of the game pre-launch and at launch led to great success for EA- at least from the start. All around, the company was recognized and this included with rising stock prices.
However, with that fame comes great responsibility. EA has a lot to live up to with SWTOR. There are expectations not only from the gamers but also from those who have invested into the company, based on the proposed success from the game.
Performance issues cause EA stocks to drop with concerns over SWTOR. This report on Market Watch explains: