I worked on an early version of a big woodworking website and it was over six thousand static html pages.
The group that acquired it needed to show progress asap, which meant simply updating the header to their new logo and footer nav.
I had to write about a dozen sequenced find and replace routines with regex to do even basic changes. In some cases groups of pages used subtly different html it was a real mess.
It took a long time for them to get all the pages replicated in a templating system to avoid seo loss.
https://forums.lanik.us/viewtopic.php?f=64&t=43148&sid=e0edf...
My task was to move all of that into a very minimal CMS. All the content would be in flat files, and the page itself would load the header, footer, content, etc.
Because every page was different, but mostly similar, I wrote an Emacs extension that let you identify the content areas (it tried some heuristics and you could guide it) and it would do the extraction and emit the flat content file and the replacement JSP file.
What you have to realize is that many people have systems that are designed for 1 "thing" and have since "scaled" that up 1000x. People still treat their website as a directory of arbitrary HTML. People manage 1000 servers like they managed their one and only very first server. It is the natural way of growth. Engineering is figuring out when that model doesn't apply anymore, and changing it. Engineering is in short supply, however, leading to stories like mine above or the "thousands of pages" blocked by EasyList.
I wouldn't be at all surprised if AutoTrader used manual editing for everything, with no access to scriptability.
Not everyone is using jekyll or any modern stacks ... the echo chamber is strong here. I guarantee you 65% of the Internet is still being edited by hand.
I once worked on a site that had over 25k pages, all hand coded HTML with Microsoft Frontpage. And all in the root folder.
Not even the owner knew how many pages there actually were.