Let's assume for a moment that google search is so good that if you have a specific enough question, then it can show 1 or "very few" results. Then "I'm feeling lucky" should be default option on search. However if it is in the interest of the search engine to show you as many results as possible, so that there are some chances you could look at something else which could lead to you spending more time there and also possibly give some business to the company. Then it stands to reason that you are asked to be as vague as possible, even if you could be specific and show you many results even if it's possible to show few. The default page should be called "Google is feeling lucky" that you might click something else and spend more time in the browser, on other websites etc.
Now it might not be designed with the motive I just descibed, but with the incentives of free search in return for attention, it could just be that the system evolved in this way.