Did you ever face an audience that clearly wasn't interested in what you had to say and didn't pay attention? Do you know what the reason was? Were you interested in and enthusiastic about the topic that you had to speak about? Did you show your enthusiasm to your audience?
You can see where the questions above are leading to. If you are not expressing interest and enthusiasm about the topic that you are talking about you also shouldn't expect that you audience will be interested and get engaged. You should be the energy in the room and express your interest and enthusiasm about the topic. This is also why it takes a lot of energy to speak in front of an audience and it is normal to be exhausted after a presentation. Express your interest and energy about the topic towards your audience to engage them. Do you want to know more about for example the preparation phase for speaking in front of an audience to ensure you have sufficient energy to engage your audience? Read the tips and tricks in the book Public Speaking Excellence that is part of the Public Speaking Kit.