QuestionWhy did only the carrot greens grow they came up nice but NO carrot?
AnswerMike:
The only reason that I can think of your carrot not developing is lack of high nitrogen fertilizer and water. The soil condition could also been a problem. It may be that you started them late and the weather got hot on you.
Sometimes these things happen. I have had the same experience but without real reason. I blamed it on the bad seeds.
Hope that some of the above causes fit into your situation.
Best wishes.
Don