"为什么你没有告诉我？"

Translation: Why didn't you tell me?

[freshprincessof]

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

[Celticfiddleguy]

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

[whitebeam3]

Why did you not tell me is also correct