I was an early user of Contentful. Before I introduced it, we had non-techies editing YAML or Markdown files and committing them to Git and deploying them using Jenkins (yeah that went about as well as you'd expect).

After countless hours supporting this system I decided to move over a couple of the content pages to Contentful (here's one example: https://issuu.com/m/success/madsounds). I didn't need to support anyone after making that move. As techies we tend to think things like Git are easy, but it's not (that's part of the reason we get paid the big bucks(

Also eventually basically all the company's CMS needs were moved over to Contentful. From my experience it scaled well for both small and medium-sized teams.

I'm not familiar with the service, why isn't a it good for individual/small/medium teams?

Why not?