Netflix has ~6,000 items to recommend to streaming customers in the US [1]. This is about 6% as much content to recommend as the DVD-by-mail service has. Their streaming catalog size is actually shrinking over time [2]. Fine grained rating systems and better recommenders aren't going to move the needle much for Netflix's current business, because they now have a content availability problem much more than a discovery problem.
[1] https://www.statista.com/statistics/1013571/netflix-library-...
[2] https://www.streamingobserver.com/netflix-movie-library-shri...