I'm not sure if I would consider 12 Monkeys 'mediocre' but at the same time I also don't consider it to be the principal point of content consumption, besides the fourth season will be its final season in 2018. Shows like Killjoys and Zoo are considered guilty pleasures and filler for those who watch them, but most importantly none of those shows have anything to do with Netflix as Killjoys and 12 Monkeys airs on Syfy, and Zoo comes on CBS. The ratings are typically the best indication of a show’s likelihood of staying on the air. The higher the ratings (particularly in the 18-49 demographic), the better the chances for survival. The Live + Same Day Ratings, which include 'live' viewing plus 'delayed DVR' viewing, up until 3am local time that same night, tend to consist of ratings marked with an "*" that are the 'fast affiliate ratings' and will be updated with the Live+SD numbers when they are made available. Usually networks get paid for 'C+3' ratings, which includes DVR viewings within three days of the original airing when commercials are watched, but those numbers are rarely released to the press though.
Netflix on the other hand doesn't typically share that kind of data and didn't cite it as a reason for cancellation, but it's a safe bet something similar was at play. After all, as history has shown us, Netflix is notorious for canceling very few of its original series. The Get Down and Sense8 were among the first and most likely won't be the last. It just goes to show you that you can have a show with noted critical acclaim and that still won't be enough. These networks want money!! A show might have a cult-like following, but if it's not bringing in record-breaking viewers, it could be headed towards the chopping block. This is actually an understandable and intelligent way for a company to run. The question that remains of course is why these more diverse series are falling flat on their faces, and the answer may be simpler than you think -- poor viewership to budget ratio.
The funny thing is that even though I try to understand the business of it all I still can't help but smh at the current dinosaur system that's in place, why certain shows get renewed, who on earth wastes their precious time watching them, why the good ones die young, and how come the majority aren't interested in watching THE GOOD STUFF?!? Honestly, I could go all day with this but it would turn out to be a complete waste of time in the end because in the near future another brain dead series is definitely going to be renewed while another great one gets axed.
I didn't particularly care for Sense8 (didn't make it halfway thru it's opening season) but I do feel your pain x10. I was sitting exactly where you are 14 years ago, March 2003 to be exact, and was one of many that actually did something about it and petitioned. If my username is any indication...