It's not an equity investment, it's a grant from a non-profit foundation.

Companies like MapBox, Stamen, MapQuest, and Bing, who have OSM layers, have an incentive to improve OSM data because it makes them competitive with Google; it eliminates the massive fixed/sunk cost of creating proprietary data and redirects the game into how you can use/distribute/mainstream that data. The business models for that are fairly clear; charging for services based on the data.

Makes sense! I didn't realize those companies use OSM. Thanks.

Google, for example, charges companies for (lots of) use of it's APIs. Maps and up to date, good quality data costs a lot.

Both are good reasons to invest in disruptive technology - to lower the cost in geodata - and to swap to a free mapping service.

See http://switch2osm.org for more case studies and information.