It recently came to my attention that there is a world of flat file Content Management Systems. I recently tested grav and was fairly impressed. The advantages I read somewhere are speed, security, easy setup, versioning control and simplicity.
But here is what I think why it is not a real suppressor of WordPress. Altough its good for a specific use case its simply not widely spread (WordPress has a quarter of the whole worlds websites). And be honest you scratch along WordPress and now learning something new again? No, thank you.
So I really can think about a few use cases but I don’t want to learn it now its simply to much while working with WordPress mainly and serving niches.