Because entrepreneurship is more highly leveraged.
Because, as Fred Wilson says, "It takes chutzpah to make it as an entrepreneur and the cereal guys can hire the CS grads from MIT easier than the CS grads can get up the courage to sell 800 boxes of cereal at $40/box." Entrepreneurship is all about sales and networking, which is something fewer people can do than engineering.
Because if you want to be an engineer, there's a step-by-step process that you can follow. It may be really hard, but if you follow all the steps then you're pretty much guaranteed to succeed. At the end of the day there are more people willing to follow this step-by-step process, no matter how hard and stupid it might be, than there are people willing to pick up the phone and call someone who might reject them.
Anyone can do hard, and when anyone can do something then by definition it isn't leveraged. A hundred years ago doing hard work was considered a virtue. Now it's a sign that you're avoiding work that's difficult.