I am asking this mainly with respect to rights. There are certain fundamental rights in India (and in several other jurisdictions ) (but I am asking with respect to India) like right to freedom and so on. These rights are provided by the Constitution. There are on the other hand other rights like those to information and right to privacy that are provided through civil law or administrative law or hounourable court's order. My question is why can't all rights directly come from the Constitution? As far as I knew constitutional law mainly deals with the functioning of states and governments so why encode certain rights directly into the Constitution while others as separate law?
First, the right to privacy derives from the Constitution, as "an intrinsic part of the right to life and personal liberty under Article 21 and as a part of the freedoms guaranteed by Part III of the Constitution", see Justice K.S. Puttaswamy (Retd) vs Union of India. The issue here is that prior to this ruling, the right to privacy was only implicit in the Constitution, and it took a lawsuit and argumentation to extend the interpretation of the Constitution. The right to information is a statutory right. The rights created by this law are stated explicitly, so no lawsuit or interpretation is required (unless a court case is required to understand what a "competent authority" is, or whether the right includes more than the 4 enumerated sub-rights). That is, this statute specifically creates a right, which could not be inferred from the Constitution.
There are three ways to create a new right. One is to "discover" that it was implicit in existing law, as in the Aadhaar ruling. Another is to amend the Constitution and add something to Part III. Turn to the Constitution itself, art 368, which describes amending the Constitution. The third way is to do this statutorily, as in the right to information. Acts of Parliament are "easier" than Constitutional amendments: an amendment requires a 2/3 quorum, and us subject to other specific restrictions, possibly requiring approval by a majority of states. Likewise the right to free, compulsory education is Art. 23a of the Constitution, but the details of implementation are a statutory creation, subject to judicial review unlike Constitutional amendments (hence Pramati Education and Cultural Trust v. Union of India (2014)).
Theoretically, the Constitution could be amended to require that all rights must be encoded in the Constitution, which would make it more difficult to create new rights.