Why don't ALL schools do what the BEST schools do? It seems quite straightforward. At least, why don't all the public schools do what the better ones are doing? Clearly there are some schools in the country/state/city that are doing well, and have become sought after by parents. Why don't we figure out what these institutions do, and get more schools to do the same things?
The list of 'explanations' is quite long.
It costs a lot of money to do what the best schools do, so that can't be applied to every school.
The best schools have parents who are themselves well educated, so that's not an option for many schools.
The best schools have great teachers, and we simply don't have enough of those to go around. And so on ...
A lot of this is bunkum. If we made an honest attempt to judge schools and figure out which ones were really performing, we would discover that major improvements could be made, but that we are simply not trying to do that.
The biggest reason we don't measure outcomes in our education system is that we can be 100% sure that if we did, we would find that we are an unmitigated disaster on all counts.
To avoid facing this truth, we have built ourselves a system that is complacent, and simply runs on a 'check-box' model - buildings, toilets, uniforms, desks, chalk, board, benches, teachers and their salaries, a few play materials, etc. If these things are present, it is assumed that education is also present. This is a mass delusion that continues all the way up to the higher universities. Only about 5-10% of the investment that we are making as a country - and I would estimate this at about 10 lakh crores a year - is productive. The rest is a kind of NREGS for the middle and lower middle classes, keeping a lot of people occupied without achievement.
If there is one reason why we lag nearly every country in the world in development, it is this - we refuse to educate everyone. It is the worst indictment that anyone can make in a society - that it cheats its children.