The reason seems obvious to me. They want to mask their lack of content. It always seems that Netflix is trying to discourage search. I guess that's because there's a good chance whatever movie/tv show you're trying to search for won't be available. Netflix only has 35 movies out of IMDb Top 250 [1]. Pretty sure the number is even less for other countries.
[1]: https://www.reddit.com/r/movies/comments/9gksft/netflix_only...