Courier is in fact the 3rd largest book maker in the US, and they have long been focused on diversifying beyond book production into other areas including content management, software development, POD, and more. And now they're getting into self-pub.
It is easy to frame FastPencil as a self-pub service but that's not the complete picture. ]It's true that FastPencil has had a fair amount of success in self-pub; they have 60,000 self-publishing content creators signed up. But the company has also been focused on working with established publishers, tech companies, and book manufacturers like Ingram, BookMasters, and B&N, as well as companies in other industries that wanted to launch their own in-house publishing operation.
Remember when B&N launched Nook Press? FastPencil was the technical partner and helped develop the platform. This was FastPencil's second deal with B&N, BTW.
It's deals like the ones with B&N that are probably the main reason that Courier was interested in FastPencil, not just the self-pub service.