FB is far from the only big tech company which has sponsored OSM as a competitor to Google Maps (Microsoft/Facebook/DigitalGlobe/Telenav/FourSquare/Craigslist have all sponsored OSM to some degree; Apple, of course, went its own way and created Apple Maps).
It's a reaction to Google Maps: a monopoly on high-quality up-to-date global maps with business location is dangerous to everyone else, as a chokepoint on mobile applications. It's less about 'acquiring data' and more about not being extorted by GM. Classic 'commoditize your complement' dynamics: https://www.gwern.net/Complement
Apple Maps is based on OpenStreetMap, and they use OSM in many countries. I believe they use OSM for turn-by-turn routing in Denmark (or was it Netherlands) (source: Apple gave a talk at the OSM conference (SotM) in 2018, but required it not be recorded).
Their motivation is self-serving but I don't think it's so nefarious. They use OpenStreetMap in check-in posts to display map data around locations that Facebook users have visited, so improving OpenStreetMap in turn improves the quality of this feature.
