"Why didn't you tell me?"
If you replaced the meiyou with bu, you would instead be saying 'Why don't you tell me?' or 'Why aren't you telling me?'
There is no 你。 The right answer is “为什么你没有告诉我”。 But there is only “你们” as an option
Did anyone notice that there was no 你 by itself, only 你们? At least for me. They accepted it, but it's a misprint.