I’m not convinced that that’s an accurate view of Wikidata. Wikidata is a basically disconnected project. There is some connection, but it’s really very minimal and only for a small subset of Wikipedia articles. Wikipedia is 99% just text articles, not data combined together.

Frankly, I think the reason people haven’t built apps on top of Wikidata is that the data there isn’t very useful.

I say this not to diss Wikimedia, as the Wikipedia project itself is great and an amazing tool and resource. But Wikidata is simply not there.