They study engineering for many of the reasons that we do: Aptitude in the preliminaries such as math, interest in the subject matter, practical applicability, and employment prospects.
There may be a couple of additional factors: Engineering has a cross cultural appeal, whereas fields such as the humanities and social sciences may be seen as solving "first world problems" for lack of a better term. And, engineering is in theory apolitical, meaning you can do interesting work without the risk of getting in trouble.
If I were a parent of a bright teenager living in the third world, I could think of worse things than sending them to study engineering in the West.