You are missing that the context here is getting through an extremely selective competitive examination. Only the top 5% students by aptitude for math/science/engineering have any significant chance of getting through. The rest are just fodder for the coaching industry selling increasingly more and more extreme and ridiculous products. Soon they might start selling products for coaching the unborn baby by teaching maths to the mother too.
None of what I am saying is intended to apply to the practice of actually being a professional engineer or having a successful career.
Is that just genetics? What about these kids' family lives? How about the interests kindled in them when they were young? How did their teachers treat them, and was there something in their experience in school, with tutors or parents which ignited a love for that subject? Did these kids' friends and family also value their learning? How much encouragement did they get?
We can't assume that kids who take the same exams differ in nothing except their genes.
They forget the investments their parents made - including sending them away for 2 years at a coaching and lodging centre - Something most folks cant afford. Or they forget that they had to appear twice or thrice. Surprisingly the entrance exam failed to recognize their genius the first time around.
I (born in Romania, was programming as a hobby since age 12) was in the "extra tutoring" group BTW, then I barely passed the maths, physics etc. exams of the first semesters, but when the actual CS courses started I got better and graduated with pretty passable grades (not that any employer looks at those)...