So it depends on the student how he/she likes and subject and want to put effort into it. If every student will master over maths, physics, and chemistry we will have lesser non-science students.
Its alright if they are not able to understand these subjects, there is a world apart from these as well.
Some students have high interest in specific subjects like math. On the contrary, 70% of the students score less grades in those subjects.
To be honest, I never scored more than 35 Marks in math from 4th standard to 10th. Gradually, after finding my interest in technology and programming, I felt the need of reasoning mathematics in programming.
Last but not least, again I agree with the author that it is significantly more for students to focus in those subjects.