1) The percentage of the population supporting additional gun control (of any kind) was around 50%.
2) The USA is a Republic, not a Democracy. The will of the majority cannot steal the rights of the minority.
3) The only "gun lobby" in this country ARE the citizens of the USA. It was because of thousands of phone calls, petitions and threats to vote the politicians out of office that stopped gun control. We vote for the people who support gun rights, and vote against those who are against gun rights.
4) The "Background checks" bill is a LIE. The bill in reality required the registration of firearms and that was unacceptable to a populace that was increasingly skeptical of their government. Regardless of what you believe, the DHS purchase of 2 billion bullets, 7000 armored personnel carriers didn't help win confidence.
5) No statistics in the US were in favor of any new gun control
6) None of the proposed legislation would have had any effect on any of the recent mass shootings, and the people knew it.
There is a reason that the Obama administration, who had a seemingly unassailable political prowess ran into a 3 ft thick concrete wall on this, and that is because the people did not agree with their viewpoints. The administration thought they could shamelessly use victims of tragedy to accomplish a political agenda that truly mattered to the population. There's Boston, LA, and Chicago, but then there's the REST of America that doesn't believe in the state and will not as readily give up their rights. Think what you may of guns, but to position gun control schemes as a just cause thwarted by lobbyists is not also grossly incorrect, but it is dismissive of the massive grass roots effort, by the people, to kill it in the senate.