I remember us once giving a supplier access to our internal bug tracker for a collaborative project. They were unable to get to the “…/openissue” endpoint.
I once worked for a company that blocked Cuban sites because of .cu (which is the Portuguese word for the end of your digestive system), but did not block porn sites (or so I was told ;-).
Are you sure it wasn't because of the US embargo on Cuba? Companies outside the US often participate(d) as well, because they want to do business with the US and US companies.
Mine blocked it when I first created it, you can usually flag an incorrectly classified site and they'll correct it (I assure that you I'm not doing any phishing).