Wild prediction here, but I think this has largely to do with their VR/AR business. Sure, having a platform to manage more spatial data is cool, but I don't think this adds
that much value to their current data.
In comparison, it could be bleeding edge for AR. There are few companies with a notable footprint in the street imagery business. Google is obviously number one, HERE has their own fleet and I think maybe TomTom and a few others actively capture this data.
What none of those companies have, however, is a flourishing VR/AR play. Zuckerberg is clearly bullish on VR/AR and Oculus is largely leading the consumer market.
This is where my prediction gets wild, Facebook intends to replicate real world environments in virtual reality. This is what OpenSfM could potentially do with enough hands on it.
I spent a considerable amount of time trying to do this myself. Photogrammetry is still in its infancy, but it works. I replicated my office in virtual reality using a phone app and Unity. I wanted to do the same with a single street, and that's how I first came across Mapillary. The technical challenge was too much for me, but I know it's possible based on literature.
Imagine doing this at scale with a network of vehicles and much improved software. You could, hypothetically, replicate the roads of New York City in a 3D environment. Imagine playing a video game in a real world environment, or simply being able to walk the streets of a place you've never been before. These could be transcendent experiences.