That's because the domain name "Academia.edu" was registered in 1999 and the current restrictions on ".edu" TLD were put in place in 2001. .mil and .gov have a

That's because the domain name "Academia.edu" was registered in 1999 and the current restrictions on ".edu" TLD were put in place in 2001. .mil and .gov have always been controlled by the US government,.and since 2013 local governments in the US may register a .gov domain.