Buildings have light switches and ceiling heights standardized because of building codes which mandate these things, and the fact that many components are mass produced so they're extremely cheap (like light switches) and are used everywhere.
Vehicles have things in the same places because regulations require it, it makes sense to do so (mirrors aren't much help if they're behind your head), and because drivers expect similarity.
Laptops are similar because that's really the only way to make them work. A keyboard over the monitor isn't usable: your arms would block your view. This is just silly.
Websites may be built with the same components (python, PHP, web servers, HTML, CSS, etc.), but that in no way means they need to look the same. It's entirely possible to make them look very different, and you only have to go to the Wayback machine and look at how sites used to look 15+ years ago, and compare to modern ones, to see this.
Basically, most of it is a cargo-cult mentality: sites update to "newer" designs that are less useful because it makes them look "fresh" and "modern" even though they waste a ton of whitespace and make the site slower and less useful. Sites used to be much better in the mid-2000s.