You're getting downvoted, but I've practiced some employment law and I'll give an attempt at some context. First, there's no one law you could really cite, because most of employment law is state law (or common law with no real codification!) But, to distill down the idea, most employers in the US will only provide title and dates of employment after a termination when asked. They do this to avoid (among other things) potential libel suits. They're also worried that anything they publicly say could be used against them in court in a different employment suit (for instance, retaliatory firing or discrimination; the exact claims can vary by state law).

I would imagine reddit's legal team advised them to avoid saying even what little they did (imagine how the phrase "we have decided to eliminate the position" could be used in front of a jury). They probably decided giving this little bit of information was good enough for PR that it's worth the potential liability risks.

Hope that helps!