Why Browsers load Websites gradually?

When I visit a website, even on a high-bandwidth internet connection, the page will load bits at a time, such that I get to watch the page be constructed before my eyes.

Even though this happens quickly, it's kind of jarring to watch elements move around. But perhaps I'm mis judging my own preferences, and it would be even more offputting if I had to wait longer for any sign that the page was loading.

Are there any studies or general UX principles that indicate why users might prefer the status quo? Is there a reason why browsers won't receive the whole page, then display it to the user for high-bandwidth connections?