Not being too rich or too poor allows engineers to become identity conscious, and being engineers they have enough analytical mind (plus time) to think & plan ways to attack the 'enemies of their religion & culture'. Remember that for bright kids in immigrant families and in developing countries, career in engineering is an easier path for upward mobility.
Lawyers and doctors aren't too rich or too poor to become identity conscious, and these professions are more typical paths towards upward mobility for immigrants.