Well, I've always tried to not look at it in just terms of intelligence. There is a lot of reasons why a person may not aspire to become "intelligent." Indeed that construct itself is something that is debatable.

The most common, of course, is ignorance. That is easy to change, simply provide the right information. The more difficult ones occur when the lack of intelligence lies in behavior. Either resistance, laziness, disinterest, or the information or skill being not considered very important.