These courses provide important services like:

TOEFL
Qualify students for higher academic betterment at foreign (American etc) colleges/universities.

IELTS
Facilitate their further studies, immigration and training abroad (Australia, Canada, European countries including the UK).

N SAT
Qualify them for entry into the best rated US colleges and also earn them scholarships.

GMAT
Qualify them for studying MBA, MBS in the USA.

GRE
Secure them entry into the MA, MSc, ME courses with teaching assistantship or scholarship in the USA.

Thus these preparation courses are effective tools for academic and professional betterment.