I think the big thing AMC has figured out is the size of the country. The networks are always trying to appeal to the masses, they seek that general appeal, and in the process make canned often boring shows. And when they try to break out of that mold they make shows that don’t appeal to their core audience (who like canned highly predictable shows) and the shows find no audience. AMC has figured out that in a nation of 311 million you can appeal to a small segment and get a huge audience. They got the economies of scale, that even if only 2% of the population would be interested in this show that’s 6 million people, and that’s not an audience to sneeze at.
Then of course there’s the vastly different economic reality of cable vs broadcast network. Broadcast networks have much higher overhead and only get to use a fraction of the day to pay for themselves (the rest being dedicated to local content), cable networks are cheap and have the whole day to put in reruns of popular shows to get that extra handful of audience. This frees them up to take a lot more risks.
True BUT AMC is drawing more audience than the Networks. They are sometimes doing in an hour what it takes one of the broadcast networks 2 hours to get. Hell sometimes they are getting triple what some of the Networks get and with a smaller overall broadcast range (less households)