My guess is that the data hasn't yet been added here in full for many movies, while most mainstream movies on IMDb have complete cast listings.

Thank you ! Isn't the data of themoviedbapi based on undocumented IMDB API ?

Isn't the data of themoviedbapi based on undocumented IMDB API ?

No. We've never imported any data from IMDB. We're building our own database from scratch.

Note: Also, some actor credit simply don't appear in the movie. I usually add whatever I see in the movie credits, and if it is uncredited, I don't add it. I don't use IMDb as a source for adding crew/acting credits, because they can be wrong (especially for crew).

For older movies where sometimes only 10 percent of the actors got a credit, adding the uncredited credits marked with (uncredited) can be very useful. But for newer movies I agree that we should focus on the actual credits. Still, adding (uncredited) acting credits is not wrong.