It is their last chance to get gun control done demographically. The demographic that grew up being fed non-stop stories of "guns are evil" by the 3 major networks is disappearing. Soon they will be outnumbered by younger people who grew up on the Internet and Call of Duty. If they don't get gun control passed now, it may be a long time until they have the opportunity to do so again.
That is why it is especially important we fight hard here. Our actions (or inaction) are going to change the course of this debate for a long time to come. The antis basically enjoyed a period from 1963-1999 where they were constantly gaining ground. 1999 was their high water mark. If we stop them here, we will grow stronger.