I've thought on this a lot. I'm not a scientist or an expert, but I can share what I think.
I think that there are a lot of small issues that play into it. First, most of the gun folks I know aren't naturally violent. All of the people I know who've went around with a chip on their shoulder, looking for fights, etc, have been non-gun folks. The gun owners I know usually want to seek a peaceful resolution to an issue.
Gun owners tend to be independent actors/thinkers. Sure, there's some group think in every group, but while leftists are pros when it comes to organizing and doing things as a group (just look at all the marches and protests we've had in the last few years) Gun owners are less likely to band together for a common cause, even if they do agree with the cause.
I also think that gun owners are less likely to drop work/family obligations to attend a rally or protest, where leftwing folks don't seem to mind at all.
This puts us in a situation where the left is always well organised, with a plan in place, and have contacts in the media to paint a pretty picture of them. The right generally has smaller turnouts and isn't nearly as organised.
Some of it is politics. Based on my own observations, left-wing politics seems to be proactive, while right wing politics are reactive. The left always gets to throw the first punch...both figuratively and literally. Its even in the names they use. Progressive= push for change. Conservatives= hold on to tradition and values.
There's a lot of guys who never experienced life before the 1930's and 1960's NFA laws. They don't miss what they've never experienced. Heck, I'm one of these guys. I've never been able to buy an SBR, machine gun, or silencer at a hardware store with cash from my pocket. I would love to be able to do so, but having never experienced it, I don't really feel the loss of not being able to do so. Its difficult to get people to protest for something that they've never experienced before.
Most guys don't want to be the proud nail either. I think most of us desire change in the way things are going, but few want to be the first one to stick his neck out. In the past, when people have asked "why aren't we protesting in DC?" I've told them that this morning I looked out my front door, and I didn't see anyone marching by. So today must not be the day. As long as the majority of us keep saying "nobody's doing it yet, so today's not the day" That day will never come.
There's a lot of risk in being the squeaky wheel or proud nail these days. You can have your career and reputation ended by keyboard warriors. Your family threatened. If it goes far enough, you could end up with a Ruby Ridge on your hands. And I don't think anyone wants to be the first one in line for that.
There have been lots of infringing gun laws passed around the US, but few of them have been passed *here*. Currently, if one takes an issue with how things are in Cali or Mass, they can always move to a southern or western state where rights are more respected. Sometimes pulling up roots and moving away is easier than marching to the capitol and making a fuss. Especially with the job opportunities found in the south these days. It can be a win-win for some.
All that said, I am seeing the beginnings of conflict in the US. Mostly through things I read on the internet. I don't have cable, and I don't watch TV. Most of the people I talk to in my day-to-day seem pretty normal, if not just a little stressed by the state of the world. But things are building and getting heated. The left is hosting massive protests. Right wing protesters are starting to organize. In a few incidents, they've come to blows. The news is filled with bitter hate and insults. We're seeing the strongest pushes for socialism we've had since the great depression, and organized mobs destroying historical monuments and statues.
I can think of a few historical events that all started out this way, and none of them were good. Something's going to happen. And I imagine it will be in the next 10 years or so.