An individual going into flight training has a wide variety of locations in which to choose. Many countries offer high quality flight training training. The single most popular location for flight training is the United States.
The USA is the birthplace of powered flight, having happened more than a century ago with the Wright Brothers. The USA has never looked back as far as aviation goes. The USA first broke the sound barrier, and put the first man on the moon. They became the leader in commercial air travel after World War 2 with a Boeing and McDonnel Douglas. No wonder so many people come to the USA for flight training!
The USA also was a wide geographical area, and a wide variety of climates. The USA has miles of coastline along both the Atlantic and Pacific Oceans, mountainous regions, and prairies. The climate ranges from sub-arctic to sub-tropical. This gives the student exposure to almost anything they would encounter in a flying career.
The USA also has some of the most experienced instructors available as well. Many have experience as airline, corporate or military pilots. In addition, the USA has the most advanced air traffic control system available, and some of the busiest airspace in the world. This gives the student exposure to the environment the will operate in as a professional pilot.