Let keep aside the issue of FII buying/selling. In the first place, do you really think that the stock exchanges are going to disclose any real sensitive data on their website? Image you are some hot shot FII/DII who is currently distributing his stock to the retail investors. If NSE tells everybody "Hey dude, this hot shot guy is selling his portfolio", would it be acceptable to you?
Large traders do not want to let anybody know what and how much they are buying or selling.
Also, if the FII/DII buying/selling data really contained any information, FII/DII would have easily influenced the stock exchange to not disclose the data; and the exchange would have obliged. And why not oblige? After institutional volume contributes almost 90 to 95% of the exchange's business/turnover. There is no way NSE can "force" any data out against the will of institutional players. If the institutional players really do not mind disclosing the data, we have to understand that the data has no value. Otherwise, anybody with a simple calculator could pick tops and bottoms based on these values.