I'm not shocked that it hasn't been a blowup hit for the network. It doesn't have the "men want to be him, women want to do him" cachet that successful shows do. Hank is just too real, you know? Tubby, unkempt, genuinely sad (In a real life way where there's no real, easy solution) and struggling to hang on and do right, even while loving how the annihilation of doing wrong. He doesn't get enough gash with women who are out of his league, he gets made a fool of and watches the richer, shallower, better looking guy ride off with the damsel. None of these things make him escapist hero fodder.
Plus, there's no over the top, porny train wreck ala Nip/Tuck or Rescue Me or even the machismo of Justified or Sons of Anarchy. Much as I like those last two shows, Terriers is so much better.