Why shouldn't academic writing show passion?

Passion and commitment are stylistic qualities that academic writers often praise in other people's writing but suppress in their own. Most academics would describe themselves as passionate, committed researchers; they love what they do and undertake their work with a strong sense of personal engagement. Many actively desire to make a difference in the world . . . . Yet these same researchers have typically been trained, either implicitly or explicitly to strip all emotion from their academic writing. What would happen if they allowed even a modicum of the passion they feel to color their prose?

Helen Sword, Stylish Academic Writing (Cambridge, Mass.: Harvard Univ. Press, 2012),  ch. 14