Everyone loves reading cartoons, and they can make great content for presentation slides (watch the copy right). But for an audience to get the cartoon, they need to be able to read it. And given the scribbly nature of cartoon fonts, fonts sizes in the bubbles need to be bigger than what usually works on a regular slide (i.e, font 20 or up). If the bubble text has to be 20 points, that means that the overall image needs to be pretty large, often you do not have enough space for it.
When creating slides that are meant for emailing in advance and reading on a screen, font size is less of an issue.
To get the audience to focus on the cartoon, chop out all the usual slide clutter (titles, footers, logos), just a plain page with a cartoon graphic. Cartoons are usually busy graphics.