You only need 1 good show that would encourage people to keep their $10/month Netflix subscription. So I assume that extremely high ratings has no particular ad

You only need 1 good show that would encourage people to keep their $10/month Netflix subscription. So I assume that extremely high ratings has no particular advantage, but they need to have very high breadth in terms of population coverage, so that almost everyone has a reason to get a Netflix account. At that point, you can calculate how profitable a TV show is, based on number of users vs cost. If you have a small but very targeted show that costs $1,000,000 to make, but it attracts 10,000 users who would otherwise never get a Netflix account, then the show is profitable after 10 months. If you have a show whose demographics overlap preexisting shows, then its value decreases, unless you can have it premier at different times of the year.