anything 可以用于肯定句、否定句和疑问句中。用于肯定句或者否定句中可以表示“任何事情/物”；在疑问句中一般表示“某事物”、“某些事物”等，而不表示“任何事物”、“任何东西”。例如：

    You can buy anything you want. 你想要什么都可以买。

    He was prepared to do anything to make a bit of money. 只要能赚一点钱，他什么都愿意做。

    Anything would be better than staying at home. 做什么都比待在家里好！

    We didn't have anything to eat for three days. 我们连着三天没吃过任何东西。     Don't do anything until we get there. 我们到那儿之前不要采取任何行动。

    Is there anything I can do to help? 有没有什么我可以效劳的？

    Do you want anything from the shops ? 你要我从商店带点什么回来吗？

   （以上例句均摘自《朗文当代高级英语辞典》第5版）

Why didn't you buy anything for yourself? 

不知有没有这样的语境？

无论从说话人的期待、还是已知的事实来看，这个句子再用anything，似乎讲不通。