“The word media comes from the Latin plural of medium. The traditional view is that it should therefore be treated as a plural noun in all its senses in English and be used with a plural rather than a singular verb: the media have not followed the reports (rather than ‘has’). In practice, in the sense ‘television, radio, and the press collectively’, it behaves as a collective noun (like staff or clergy, for example), which means that it is now acceptable in standard English for it to take either a singular or a plural verb.”
https://en.oxforddictionaries.com/definition/media
The word is borrowed from Latin but in English we do not slavishly adhere to the foreign rules and meaning. And no, decimate does not mean “reduce by one tenth” in English as it does in Latin.
I was not aware the official rules of language had been reduced for the benefit of the lowest common denominator.