Seems to me the blame lies mostly with the Republicans and the NRA. But the fact that the Dems were unable to control their caucus brings up a reasonable theory:
Among those who maintain nothing ever happens in the House by accident, there.s another line of speculation. Failure to pass the bill may help the Ds as a whole avoid a firestorm of grass roots activity from enraged gun owners and the National Rifle Association. That might have spelled trouble for them in the next election. And so the whole big show helped them dodge a bullet so to speak.