Welcome to my stream-of-consciousness essay on the history of typography and its relation to modern literacy!
A site's choice in typeface might be something that's only noticeable to you if the font happens to be particularly difficult to read, or one that you have a personal adverse reaction to. Think Comic Sans, Curlz, or Desdemona. But even if the choice in font is not immediately noticeable, there is a high likelihood that choosing that particular typeface style was carefully considered, even if you don't instantly have a reaction to it.
Typography has a rich and interesting history that dates back to the first typeface being designed by Johannes Gutenberg in 1439. (Moveable text based in bronze and metal had been around for centuries longer than Gutenberg in East and Central Asia.) Letters were individually designed and carved into lead, and were used in creation of the first printing press. Prior to the printing press, all existing text was hand-lettered, usually in Latin. These texts were mainly religious texts, were costly and hard to distribute, and subsequently stayed within the ownership of the church. Lending libraries too, although extremely rare, were usually restricted to the educated and upper-classes.
An aside worth exploring, but one I won't go too in depth with here, is the rise in literacy that exploded when printing presses made documents, news letters, and other important information able to be easily distributed to the masses. Until printing presses became the norm, it wasn't uncommon for an individual to go their entire lives without learning to read or write, or even look at a book. Books, after all, were usually illuminated texts commissioned and owned by the church. Scribes, as some of the few educated members of society, were few in number and, because religious organizations had the means to commission costly texts, scribes didn't often extend their services to creating information for the public.
The history of typography is vast and rambling, but puts our current ability access to information in stark perspective. Think of the incredible amount of change that had to take place in society, technology, and education for us to simply be able to choose a font and start typing in any style of our choosing. We often imagine learning to write by pen or pencil as the picture of literacy, but what would it be like if you couldn't type? Typing equals being able to spell, which equals being able to read. Our choices in typeface can be philosophized down to such a basic level. Sans serif fonts are hailed as the gold standard for computer-based typography; if you can't read, sans serif or serif fonts aren't going to make much of a difference.