Why are ancient greek and latin often called dead language?

For the answer to the question above, A language is considered dead if it isn't spoken by a group of people anywhere in the world as a dominant form of communication. Latin can be learned but it's not a language that people socialize in anymore. It's really only a language of the Church and even academia.
Classical Greek and the Greek before Classical as well as Koine Greek is all dead. People don't speak it or read it anymore except in academia. A modern Greek would not be able to understand Classical Greek just as we who know English can't understand Old English without learning it. Latin evolved into Italian. An Italian could not understand Latin without taking courses in it. But I think personally there is no such thing as a dead Language. As long as texts from the language survive and there are people who can read them a language lives.

Hello there.

Why are ancient greek and latin often called dead language?

Because hardly everyone speaks the languages communication.