While such an important question merits a much detailed and comprehensive approach, here is something that you might consider relevant especially if you are just on your morning coffee on a Sunday and you just want to ponder over it. In other words what I am going to write is perhaps a terse but lists one of the most important factors, and in my defense its just a blog.
Why India does not achieve academic excellence, I will just give example of one primary reason: arbitrary rules wrt qualifications, merit, skills, caste, age, time line.
For a glossary of certain terms which are nonetheless self evident (at-least for an Indian audience) you don’t need to scroll to the dead-end. Here they are; PG: Post Graduate, UG: Under Graduate, NET: National Eligibility Test, SET/SLET: State Eligibility Test, B.Ed.: Bachelor of Education, M.Phil.: Master in Philosophy.
qualification: it has always been arbitrary. We are not sure whats enough or adequate to teach. Sometimes a person with PG isn’t considered good enough to even teach in high school or junior college, without additional degrees of any moiety of relevance. Sometimes lower qualifications than PG are fine for teaching such classes, with (mostly) irrelevant degrees or qualifications. eg someone with B.Sc.and B.Ed. is qualified to teach high-school but someone with PG, or PG+PhD may not be qualified to teach high-school or junior college, although its fine for him/her to teach senior college with a PhD. Also with PG qualification you can’t teach UG. But with PG, one entrance (NET/SLET) can decide your qualification to teach both UG and PG. I am talking about basic minimum qualifications. So you are not considered qualified without certain irrelevant factors. Its not like you are considered and given a time line to achieve any required additional qualifications.