What we think of as writing is hard without the right technology. You need parchment/vellum/papyrus, and something to make ink, and something to make pens with.
None of this is trivial. And it's not obvious until someone invents it, or is told how to do it by someone else.
So you can have an alphabet - but if it's only ever engraved into rocks, that guarantees that whatever gets written is really, really important to someone, and there won't be a lot of diarising, philosophising, or gossip, or even recording of battles.
The fact that we can buy pens, paper, and digital keyboards so easily we take them for granted is actually kind of amazing.