This is because (deliberately or not) what the speaker often wants to communicate mainly is that they are smart. Getting everyone lost in the first five minutes

This is because (deliberately or not) what the speaker often wants to communicate mainly is that they are smart. Getting everyone lost in the first five minutes is not a big problem, quite the opposite. I have seen young people who gave brilliant lucid and comprehensible talks who were criticised by the experts in their narrow sub-field as "popularisers". I think many people know how to give a great talk, but choose not to.