Hello Hidayathulla,
Your query is more than technical. To me the reason seems to be related to several factors of SAP architecture like optimization, constraints, initial decisions, different groups handling different tasks while developing etc etc. In SAP what you have asked is just one example. While working you come across several such similar Whys.
Also your query can be modified by replacing CS by PM/CS .
Wish you get more satisfactory replies. (The probability for this might lie in ABAP space)
Good luck
KJogeswaraRao