>Sure! But what else are you going to do if your document uses a super-special font for displaying mathematical symbols or sanskrit or the glyphs of a language understood by fifty people on the planet and Unicode isn't widely adopted yet, having been invented just two years before PDF?
Assuming it's for print/display and not future editing, I imagine you could convert the font strokes to vectors or similar.
You could. But in a thousand page document, that's a lot of memory used up to record a vector for every letter 'c'. So of course you do two layers: record modifiers and transforms on a canonical 'c', and then keep a canonical 'c' somewhere with all the other letters.
... But you already have that data structure: it's the font file itself.
(Possibly worth noting here also is that historically, Adobe owned both the PDF format and the file format for most popular fonts. So they were heavily incentivized to just reuse code they already owned here instead of reinventing a wheel).
In fact many PDFs still do convert the text to shapes rather than use the font. It does cause problems when you need to copy text out though