Japanese term (edited): ���q�l�̌l���o�^�̖ړI

As I asked you in the "qustion to the asker" I am not sure what you are looking -- translation or reason why the site is asking such information. If so (i. e. the latter) I have no idea but you know they do that all the time (and hopefully in encrypted manner).
Like anything else nowadays they want our personal info. for "marketing surveys", "to improve our service", or else who knows. Buyer beware!!

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Note added at 3 hrs 49 mins (2005-01-26 15:02:51 GMT)
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You can use \"the purpose\" in place of \"the reason\".

Japanese term (edited): ���q�l�̌l���o�^�̖ړI

Assuming that you are looking for a second opinion on your own translation ("WHY THE USER HAS TO PROVIDE THE WEBSITE WITH HIS OR HER PARTICULARS"), I think that this would be a more appropriate translation.

While your proposed translation is not incorrect, it is a bit awkward and could seem slightly below register for what I assume to be a disclaimer.