What do you think are the reasons for the extinction of languages?

The people who speak it may be exterminated by invaders (Aztec, Mayan) or the language gradually changes (Sanskrit,Latin-> many European/subcontinental languages). Latin is formally extinct (nobody speaks it as a native tongue) but because of its enormous influence in historical times it is still used in specialized areas, and some people can actually use it as a common language between individuals who do not know each other's language. So from some point of view it is not yet extinct.