August 11th, 2006, 2:29 pm
because the model is1) a member of the class of affine process which have very useful properties. Including nice clean analytical solutions to some pricing problems.2) qualitatively similar to behaviour of actual price series3) better than any of the alternatives - the alternatives either don't resemble the actual price processes or don't give such pretty solutionsif this is too simple for you, try jump diffusions.