It should be considered disrespectful to waste everyone's time by giving a talk that is super difficult to follow and basically unintelligible to anyone in the room who doesn't work on the exact topic being discussed. There is a perverse incentive to deliver unintelligible talks because the audience just assumes the speaker is too smart to deliver the talk in any other way and often believes they themselves aren't smart enough to follow. Moreover, this format shields the speaker from having to answer any thoughtful questions at the end of their talk because only those who already understood everything could follow along. Over the last three years, I've probably attended over 100 hep-th talks, and this is a chronic issue. Everyone in the room has the intellectual capacity and background to understand what the speaker is saying if only the speaker would actually deliver their talk at an appropriate level.