Have you ever read a “magazine”? These were pre-internet things that were printed on paper, and included text and images. Often these images were illustrations, rather than photographs. They break up the text walls, attract the eye when you’re flipping through deciding which piece to read, and create a mood.

As to why the images are so huge, well, nobody gives two shits about download size any more in a world where you’re also probably pulling down multiple megabytes of ad images and JavaScript because every damn webpage has to be an app even if it’s purely static content nowadays.