The Path
Perhaps the greatest obstacle to success in modern life is a sense of futility. If one is going to put a lot of time and effort into doing something, it helps to trust that it will pay off. (This is something that I find to be missing from a lot of talk about "grit." "Grit" in the face of certain failure is viewed as quixotic, rather than determination.)
One area where I see a sense of futility consistently at play is in left-leaning politics here in the United States. Broadly speaking, the American Left has, among its policy priorities, maintaining or restoring access to legal abortion (and contraception more broadly) and reducing (if not eliminating) the access to personal firearms. These are areas in which they've faced opposition from the American Right, and, broadly speaking, the Right has been winning this contest. It's likely that, despite rhetoric about allowing states to decide their own abortion policies, that when Republicans take control of the House of Representatives, someone will float a bill to criminalize abortion nationwide, and some of the very people who claimed that it should be a matter for the states will vote in favor of that. (They'll have their perfunctory responses to the knee-jerk accusations of hypocrisy at the ready, of course.) And it doesn't even require having paid any attention at all to the "debate" concerning gun control in the United States to realize that it's going nowhere.
The general reason for this is the phenomenon of the "single-issue voter." While these groups of people are minorities of the overall public, they have the ability to make it difficult or impossible for people who don't toe their lines on their favorite causes to be elected. Make them unhappy, and they walk away. And there's always someone who will rush in to tell them whatever it takes to obtain those votes. And if they want to stay in office, they're forced to walk the walk, at least enough to avoid leaving room for someone to challenge them on the basis of greater adherence to the party line.
The American Left has no such groups of consistently motivated voters on its side. And I think that they've mostly given up on attempting to cultivate them. Which I will admit that I find to be strange. Because the current strategy of appeals to majoritarianism (when it suits them, anyway) and the ideals of democracy aren't getting them anywhere. So, for instance, while there are a number of people on the Left who object the idea of billionaires in concept, as a matter of both ethics and economic justice, the chances of altering the business regulatory environment to eliminate the economic incentives that create the consolidation of wealth are functionally zero. There's something telling about the fact that it was considered more likely that disaffected right-leaning voters in the United States would manage to install a government that would dismantle America's republican form of government during the most recent election cycle.
The question of why the Left tends to be more focused on the idea that "somebody needs to do something," and holding street protests to that effect, rather than coming together as a block of voters and emulating the tactics that the Right has successfully deployed again and again is "above my pay grade," as they say. I suspect that it's another facet of the broader coalitions that make up the American Left. It's hard to get half a dozen people to all agree to what they want on a pizza. Getting a few million people to all agree on political priorities is no easier. And I think that this is the part that's become lost to a sense of futility: the idea that a set of priorities can be created, and the boxes ticked off one after the next. The American Left has the population needed (although there may need to be some shuffling of where people are actually located) to push through legislation on guns, abortion, billionaires or what have you. They need to trust one another to go down the list, rather then people bailing out once their pet project has concluded. This, perhaps, would give them a greater sense of the power they could wield.