Some graphic designers with a knack for using animation software will take all the elements of a normal web page and put them into an animation file rather than a picture file.

It's the old “When you have a hammer, everything looks like a nail” situation that existed in the early days of the web, when design options were very limited.
Illustrators figured websites would be elaborate illustrations. Animators envisioned websites as animations. Neither was wrong, it's just that those familiar individual preferences have become out of date because the internet has evolved so much.
Modern websites can include text, pictures, video, audio, animations, and more. They all have their place, and to build an entire website in only one medium is unnecessarily limiting to users. The choice should belong to the user, and, for example, not alienate blind or deaf visitors due to content they can't experience.
To be fair, in both cases (a "web page" that's either a picture or animation) it's often the design and animation software that is largely to blame, by having misleading options like "export as web page" or "export for web". These are handy software features, and perhaps suitable for personal web pages, but certainly not for business websites that need to be built to maximize search engine comprehension, accommodate all users on all devices, and correspond with how the internet works today.