You can do lazy image loading in just a few lines of javascript, without jquery. Scripts can be deferred, etc.
Those are hacks. I'd rather have a browser that loads stuff really fast and not have to jump through hoops like spriting, etc. If you're really concerned about deferring the loading of images, that could also be a feature of the browser.
Also, consider that asking the question, "why the heck would anyone develop a website that loads that many elements all at once," is like asking, "why the heck would anybody develop a program that doesn't fit on a 1.44MB floppy?".
HTML is a declarative format, so the presence of an <img> tag doesn't mean it has to be loaded eagerly. You could turn it around and ask why the browser is loading assets that can't be seen.
Also, consider that asking the question, "why the heck would anyone develop a website that loads that many elements all at once," is like asking, "why the heck would anybody develop a program that doesn't fit on a 1.44MB floppy?".