One Reddit user claims that this is how Reddit avoids CSS clashing. If one component uses .title to name a specific post, for example, then another uses .title to name the sidebar information, Reddit's web designers would need a much deeper scope. Otherwise, there would be a clash in the site's CSS coding. Reddit most likely uses .title, then randomizes another class name when pages are built.
Little to no performance is lost by changing the class name from .title to using CSS modules, but the real advantage to Reddit's approach to class names involves less overhead regarding style names and conventions. This method requires no use of BEM CSS, and, in fact, using BEM has the potential to run into name clashes. In this case, you would use the class name, .item__title--fancy, then someone else will use it too. In order to avoid using longer class names, which will negatively affect a site's performance, you can opt to use CSS modules, wherein web designers don't really have to care about the issue as much. For more information click here https://www.reddit.com/r/web_design/comments/aat7l7/why_are_class_names_so_weird_on_reddit_website/.