Question

why we accept the constitution even after many years of independence ​

Answer 1

So asking why are we following a constitution that was written 67 years ago is almost equivalent to asking as to why are we following the 1000 year old tradition of bathing in the morning and sleeping in the night. Certain things have acquired the status of gospel truth. Because, years and years of experiments in certain fields have led to saturation of wisdom in those field. Such as the self government or democracy.

Now it is almost universally accepted that democracy is the best form of Govt. (With some reservations of course).

Besides ever since the constitution was accepted, it has undergone more than 100 amendments. So it not exactly the same constitution that was written 67 years ago.