To put it simply, slides aren't handouts. Slides are meant to work with the speaker and help the audience understand when showing is more efficient and effective than simply telling. Examples of this include photos for visual imagery and charts and graphs for data.
Handouts are for audience members to take home and read at their leisure so it doesn't matter as much if each page is jam packed with information. That being said, no one enjoys squinting at tiny font when trying to read the bottom corner of a busy slide that is showing 18 different things.
Last week when watching one of the pitches, there was a particularly busy slide that the presenter showed but only chose to talk about one section of it. I asked him why he put so much extra information on the slide but didn't bother to explain it. He seemed surprised that I would ask. The next slide was also packed with information in various formats and it took him quite a long time to cover everything. In this middle of his detailed explanation, I asked him where my eyes should be on his slide. Again, he looked confused. He was missing two important aspects of slide design. One: if you don't plan to say it, why show it? Two: information needs to be given in small amounts.
There are many other mistakes that presenters make with the slides. They write what they are going to say and then read from their slides. They fail to use animations for lists. They turn away from the audience and talk to the screen. But for now, let's focus on the process of sitting at your computer and designing a slide. Ask yourself what you want the audience to focus on and build a slide around that. Giving information to an audience is like feeding a baby, you need to give small bites and time for digesting is needed. Your slides will have much more impact if they focus on one thing each and what the audience is hearing matches what they are seeing.