The beauty of using a static site generator is that your back end can be completely separated from your front end. You can easily swap it out at any time no questions asked, and that's exactly what I did with Learn Build Teach. I went from markdown files to a true headless CMS in Cosmic for my courses information.
Why would I want to make this shift you might ask? Well, by completely decoupling my front end and backend, it gives me some flexibility. I have the ability to swap out my backend at any time as I mentioned. But also, it gives me the ability to leverage that data on multiple different front end applications.
Additionally (and this is the big sell for Cosmic), if I am going to have non developers contributing to my content, they get an easy to use GUI to update information. Writing markdown files isn't extremely difficult, but it certainly can be tricky for people that are new to it. With Cosmic, anyone with access can easily create/update content in a comfortable environment!