Update: The longer I use this flatfile CMS that I use for this site, the more I like it. Typically when you change something behind the scenes using CSS (the bits of code that instruct your browser how to lay out a site), something else suffers - especially with WordPress and other blog and CMS software. With this CMS, cmsimple by the way, from the installation (upload the files and you're done) to changing the CSS, everything works the first time. There isn't the half a day debugging half a dozen things just to change the position of bit of text. Another thing I like about this flat file system is that not only is it fast, there aren't php or CSS issues any more. You might notice that sometimes web sites don't display correctly and you need to reload it. Yahoo is famous for that. With this flat file deal, I have had no issues at all with any aspect of the behind the scenes workings of the site.
The reasoning behind choosing a flat file CMS (Content Management System) is simple. I need a site I can edit with ease from any device. While I've been using traditional systems like WordPress for a long time, becoming a sort of WordPress savant, all WordPress sites need a slew of what are called plugins which give WordPress more capabilities. This of course creates additional things WordPress needs to do when displaying a page to the user which of course causes the server to slow down as it processes all of these bits that the system does to display a website to you. And there are also calls to the database which also creates additional loads on a server. All of these things create a load on the server that the site runs on which in turn slows things down.
And to make matters worse, a normal account that you have with the company hosting your website uses server sharing where dozens if not more websites are running on it at the same time which (of course) causes even more load on the server which slows it down even more.
So, most WordPress sites run a file cache system (which creates a unchanging file that is shown to the visitor instead of all the database and plugin reading that it does) that it shows you instead of the "real" site. These are called static files. Of course the system needs to build the unchanging files once in a while which creates additional loads on the server which slows it down even more.
That said, it's interesting that on a WordPress site you strive to create a static file of a page for faster loading when you could have just eliminated most of the stress on the server by not using WordPress right from the start.
The database being referenced a lot is one of the largest reasons a website slows down. Of course when you have a gigantic site like (for example) Foxnews or CNN or Breitbart, using a database makes more sense so most of those sites run on something like WordPress. Then there's the complexity of the coding (which is the programming of the site, usually PHP and HTML) which can cause a lot of errors on the server which slows it down even more.
A site like Drudge which is nothing more than a bunch of links with a few other pages can run fine as a flat file system. This site, altrightnation.com is similar to Drudge in that the only page that isn't static, unchanging is the news headlines page which changes often.
Most of this flat file stuff assumes that you don't need to have a bunch of relationships between items on a website - which would need a database to function. An example of this would be a recipe site that has millions of visitors and bunches of traffic from searches. An example of a site that doesn't need a database system would be a restaurant website with their menu on it and an occasional recipe or two as a blog post. What it all comes down to is speed. A flat file CMS that has medium traffic will be far faster than a database driven site.
Of course there's a caveat staring at us - there is only an X speed you can get from a database driven site - that's why a cache system is normally used.