[lancefisher]

It’s a data driven decision. They a/b tested and found users were more interested in clicking on ads when images were lazy loaded.

[viraptor]

Or a more mundane reason: You need to add the dimensions to the image to reserve the page side and prevent skipping. That takes extra effort and is not something people think about. If there are any places that a/b tested changing layouts specifically, I expect it's extremely few. It's much easier to make the background a clickable ad area and some pages do that explicitly.

[kwhitefoot]

Why does anyone need to add the dimensions? Surely the build process can do this ahead of time or the server can do it on the fly. It only needs to be thought of once.