Why aren't record/replay debuggers more common?

Record/replay debugging seems like a powerful concept. Being able to record execution and then replay it later to investigate bugs sounds useful, especially for difficult-to-reproduce issues. Why don't more programming languages have mature record/replay debugging tools? For those with experience in debugging tools: - What are the biggest technical challenges? - Which languages would benefit most? - Are existing debuggers already good enough for most developers? - Is there limited demand for this kind of to