I'm no expert but I think it's because of two main reasons.
One, as I described earlier, these people see jews entirely as organized outsiders. Jews make up their own community that often isolates itself, follows its own rules, is apprehensive about the rest of the world and has its own interests / customs. Despite having lived in the US / EU for generations, they're still different from "the norm" in many ways that, say, Catholics are not. This status or standing as outsider is what makes it different from the examples you gave. It's not so much about what
they do (the lobbying, the financial influence...) but about who does it. Groups like the NRA (pro gun) / Bloomberg (pro gun control) might do the same thing but they're seen as the product of ordinary American interests protecting the rights / lives of the normal masses - even when it's a position they don't agree with. They're seen people from within "the group" trying to accomplish a good (but perhaps misguided) purpose. Yet, in the eyes of anti-semitists, jews work in their own interest. When they lobby or exert influence, they're seen as doing it for illegitimate foreign purposes. They don't act in the interest of the people (or for acceptable American corporate reasons), but they do so to further their own external agenda and power. The jews are "They" with the capital T - a faceless yet powerful collective with a selfish external agenda that directly goes against the interests of "normal people" whereas the NRA are a product of the common folk.
Two, because antisemitists consider many things associated with Jews to be inherent to them as people. "The jewish people didn't do well in banking and finance because of the circumstances that allowed them to do so. They did so because they're all inherently greedy and selfish. Jews didn't play a part in the death of Jesus because that's what people did to unknown threats back then. They did so because they're vile and untrustworthy to their core. Jews don't stick to their customs and their own people because that's what many cultures do especially when they've faced a lot of backlash. They do so because they're antisocial scheming elitists. Jews don't still talk about the holocaust because it's a case of horrible genocide that happened only 70 years ago and is still survived by people alive today. They do so because they're filthy parasites leveraging tragedy and guilt to disenfranchise others."
I can go on but you get the point. The NRA and its supporters are just people you might disagree with or who might be acting out of selfish reasons. But Jews are seen as a race of outsiders that act exclusively in their own interest at the expense of the rest. A race with a whole lot of inherent undesirable attributes they all possess (hostile, elitist, controlling, scheming, antisocial, betraying, untrustworthy, greedy, selfish...) that's either a threat to others (as they're so powerful and often said to be "the chosen people") or a burden that will keep the rest down (as they're leeching parasites who have nothing to offer other than scheming and preying on others). These views and their history makes them a very convenient scapegoat and easy to hate all over the world, even today still.