"为什么你没有告诉我？"

Translation: Why didn't you tell me?

[freshblair]

Should "why don't you tell me" be accepted too?

[neekee]

没有 is used for past tense negation, while 不 is used for present (and future), so "why don't you tell me" would be "为什么你不告诉我" (I'm not a native speaker though so someone please correct me if there's any other issue with that sentence!)
https://resources.allsetlearning.com/chinese/grammar/Bu_and_mei(you) lays it out nicely with some more examples. :)

[domsalazar0]

Wow, I've never heard of 没有 vs 不 denoting tense. That was very helpful, thanks!

[lorigkvack]

Look at the tips in the lessons :p

[Kivolamuzikisto]

You're absolutely right.

[Hedwigechouette]

no, because the 没有 indicates past tense

[Hedwigechouette]

"why haven't you told me" was rejected but I think is equally fine

[JJCastro11]

因为我.....我.....我..... 没有时间啊！！！

[whitebeam3]

Why did you not tell me is also correct

[CookiesSloth3910]

为什么不告诉我？

景琰，小殊对你的期许与他人不同，你明白吗?

我就快认出他来了。我应该认出他来的！！！！

来，起来。
景琰，现在仍然没有到你可以伤心难过的时候。前面还有很多事情要做。你和他都不能停下脚步。
他病得中吗？

我只有一句话：完成他的心愿。这也是你的心愿。我们所有人的心愿。

[Gelukservaring]

Interestingly, the object "it/that" is left implicit, just like in English.