Well, it's cause a rounding error of Democrats aren't going to vote for an otherwise ok candidate if they don't support tougher gun control laws, while a non-rounding error of Republicans supports would probably not support a Republican candidate if they did support more gun control.

Put another way, I think it's fair to say that the majority of people who care about enacting stricter gun control, also do not put it in say... the top 5 issues, especially at a national level (loosening gun control laws might be otherwise). The converse position is true on the other side. I don't think there are many gun fans who would say... "repeal the NFA" as a top 5 'must have' position. But "national semi-auto ban"... well, that's like a top 5 position right there.

Put another way - would you have preferred Obama to enact ACA, or stricter gun control laws?