I tend to find a lot of the folks coming out of online or bootcamp-level courses start off as front-end or app (usually web app) developers, and then gradually pick up the backend and architecture pieces as they grow as a developer.

There are also simply those who want to pick up these skills and apply them in their job -- one of the Thinkful students I mentored was a GIS data analyst who just wanted to be able to write scripts around the data he was working with.