This was a question from a friend of mine. She said "Drives me bonkers".
I replied and told her its "because they can".
But if this is you and your website, make sure you put yourself in the shoes of your viewer.
Movement makes it more difficult for the viewer to read, its distracting. An example is image slideshows on home pages - viewers don't hang around to watch your images and statements, they move on to find the information they are after. So use one image and one statement - but make the image stunning and relevant, the statement succinct and sharp - with a call to action if appropriate.
If you have something you want to announce, or state - do it succinctly, and without movement - so your viewer gets their information quickly.
Focus on one announcement for the week (one image) - and then change the focus the next week and make your second announcement.
You can then use that focus and imagery on your social media platforms, highlighting your announcement.
"It’s so hard to bloody see anything. They move too quickly and it’s just very frustrating."