what gives?
I don't know—it works for me.
This plugin uses the provided API to retrieve data. If it's like it's sister site TheTVDb, it's probably not searching the live site, but using a provided data file. If so, that might not be up-to-date. Or they may intentionally exclude movies that haven't been verified by enough people (note it has no rating and 0 votes). But that doesn't explain why it works for me.
Don't expect TheMovieDb to ever be anything like IMDb. I can't imagine anyone using as a preferred source, and if you use both, you should be careful about mixing credits data. It may have bits of data you prefer, like it's overviews, posters or fan art.