Why do "big" companies' websites are so complicated? [closed]

Companies such as Google, Facebook, and/or Reddit have websites that are so complicated.

For example, normally when importing style/css we just do it this way:

<link rel="stylesheet" href="some_style.css">

But, when you look at Google.com you see this:

<style data-iml="1593762511208"> some style inside it </style>
<style data-jiis="cc" id="gstyle" data-iml="1593762511208"> much more style inside it </style>

I mean, why they use such complicated way to just add CSS to website? What does these mean?