@Jerry 

Broadly speaking, there are two types of university entry requirements: hoops to jump through and requirements that actually make sense. If you're required to have high math grades in order to study a foreign language, or high history grades in order to study engineering, then that's (mostly) just a hoop to jump through. If you cheat, then you cheated, and that's dishonest and unfair to others, but at least you didn't shoot yourself in the foot! But if you cheat your way to high math scores and then go study engineering, then you hurt yourself because next thing you know, you're failing all your classes. It's the same with English proficiency exams: if you cheat your way to a high score, then you'll pay as soon as you set foot on campus, even if nobody ever finds out that you cheated. 

@Jerry 

"I know it's rhetorical but it's because we all know that people the world over are looking for a shortcut in every area of life." 

Well, yes, except that it's only easy until you arrive on campus and start floundering! 

"But I always thought that all institutions of higher ed have their own proficiency exams that they administer before admitting a foreign student. Maybe not?" 

Nope. They generally rely on standardized tests such as the IELTS or TOEFL.