Why do people learn English? Because it is world language. It is the second language of the world of speakers. If you can speak English, you can travel in many countries. Your journey will be full-fledged (полноценный). And more than that if you study English, in future you will be able (У тебя будет возможность) to get a very good and well-paid job, because English is necessary for many professions.
Which is why (Вот почему) people learn English.