It actually wasn't though. The cast seemed to hit their stride in Season 3. The show suffered early on from bad casting. Ruby Rose was a shit lead and apparently Dougray Scott didn't really want to be there. With the two lead actors having so much bullshit going on between them, it took the writers a bit of time to dig themselves out of that hole narratively. But by season 3, they were out of the hole, they had the right cast to tell the stories they wanted, and were able to make a pretty decent show. I don't think they were dead last in the ratings but then again this decision doesn't seem to have been due to ratings it was mostly network politics.