The Netflix Prize competition launched in 2006, before they had started streaming anything. The problem was to recommend a huge DVD-by-mail catalog to millions of users. By the time the competition finished in 2009, streaming was already growing rapidly. Nowadays their DVD business is a small footnote to their streaming business. The streaming catalog is much smaller than the DVD catalog and the consequences for starting to stream a show/movie you don't like are much smaller; you can back out and immediately start something else. You don't have to wait days to return your unsatisfying DVD and get a different one in the mail.
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.
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...