Because we can! Games were slim back then because they had to be. Webpages are fat now because our computers are fast.

Now, if a webpage were to approach the size of a contemporary game...

The biggest culprits are the layers of Javascript for and and tracking/analytics and unoptimized, high-resolution images and videos...

http://idlewords.com/talks/website_obesity.htm

More because that "whole game" was incredibly small, not because a web page is particularly big.

A single good quality jpeg is around 1MB. If you have 2 nice pictures on your web page, suddenly it's bigger than doom.

For one, Javascript is used as source code text, whereas games benefit from being compiled to binary form. There's also a monetary cost for file size if your game requires two floppy disks rather than one.

Because modern web sites circumvent the HTML engine and request JSON from the server which they then render via JavaScript.

Other bugs with the modern web authoring style:

1. broken back/forward functionality

2. broken scroll bars

3. broken accessibility

4. broken memory of where the page was at when closed, leading to a fresh load of the page on Re-Open-Closed-Tab

5. infinite scroll being highly unnatural

A simple web page nowadays is bigger than a whole game in 1993. A whole budget game nowadays is several gigabytes in size and that is far from a simple website.