While we know that wasn't actual full frontal nudity, I think networks - broadcast and network - would deem it as such and thus have to edit or perhaps blur it out. Premium cable, increasingly, has no issue with full frontal, but, as Zegeekgirl pointed out, they desire to produce their own original programming, which would leave streaming services like Netflix and Amazon as options for the show.
In defense of US television, I will say networks, censors and the viewing audience seem to be loosening up. Though, I'm sure with the networks, a lot of that has to do with trying to compete with cable and streaming services to which they are losing viewers at an alarming rate. Some forms of nudity, swearing, sex and graphic violence are becoming much more commonplace on TV shows. I watch 'Hannibal' and, even though it's on at 10 pm, I'm still shocked at what NBC, a broadcast network, allows to air.