Excellent post, Freethinker. All of those factors are a big part of it, the two party system being the biggest one. The two monopoly gangs work together to deny "third" parties a fair shake due to extremely unfair ballot access laws, media blackouts (or smears), and campaign finance laws which are tilted toward the Republicrats. One would think in a system in which "equality" and non-discrimination are held up to be the highest goods, that this would not be the case when it comes to ballot access, but the courts (Democrat and Republican judges) routinely uphold the various state ballot access laws that don't allow for a level playing field. The U.S. has a closed, rigged political system much closer to a traditional one-party state than an "open democracy."
The size of the country is also a big factor, but a party or political organization needs to concentrate on organizing at the local and state levels. Even in a relatively small state like Pennsylvania, an event held in Pittsburgh is a 600 mile+plus round trip by car for someone from the Philly area and vice versa. I know because I lived it, going to literally hundreds of Populist Party meetings locally, state-wide, regionally and nationally in the 1980s and 1990s. "We" did have a party for a while that was formally organized in almost every state, ran balloted candidates around the country every year, and had two presidential candidates who were on the ballot in 13 states in 1988 and 16 states in 1992.
But that fell apart for reasons I'm not going get into here, and since then, nothing for 20 years until the rise of the alt-right. I kept waiting for those young rays of hope to leave the safety of their computers and become active, and they finally did, culminating in Charlottesville, the aftermath of which continues to be an ongoing disaster for them. I wanted to see them organize politically rather than engage in direct street action, but I understand why they did what they did and after 20 years with no political vehicle the art of organizing and being active on behalf of a right wing third party no longer existed. There was no template for them to follow and I also understand why so many of them detest the "boomers" and older folks who totally dropped the ball. There are very few people left now who understand how to organize a minor political party as well as deal with ballot access requirements. More recently I was the Executive Director of the American Freedom Party for several years, but left them in 2014 after it became clear most of the leaders had no idea what they were doing and had no intention of learning. The American Freedom Party is a "party" in name only, nothing more than a website.
Building a political organization is a mostly onerous task which requires one to willingly accept failure for a long time in the hope of eventually making enough incremental progress to have some breakthroughs, thus becoming well-known and a force to be reckoned with. But it's not possible now, for the reasons you mentioned and others like doxxing, antifa, and the alliance of government, law enforcement, the courts and communist thugs that bared its fangs at Charlottesville. In 1988 we were collecting signatures around the country for David Duke to be on the ballot as a presidential candidate. Can you imagine what would happen today if Duke or say Richard Spencer were running and their supporters tried to collect signatures for them? It's just not possible now. Similarly, of the hundreds of Populist Party meetings I organized, only a few had to deal with on-site protesters and thugs. It was a different time, and all of the ills we were battling against back then have only progressed that much more.
That's why I often express my frustration at the lack of organized fightback by White Americans, any fightback at all really, when we see it taking place all over Europe, where they too have to battle against entrenched laws and political parties at a decided disadvantage. I also see how much the war on dissent has accelerated under Trump; it's very real and if we haven't passed the point of no return for Middle America we are very close to it. A very strong argument can be made that the demographic trends of the past half-century are now irreversible and the only real question left is just how small a minority Whites are going to become in what until recently was always our own country.
So yes, Trump is a big phony to me to put it kindly, the "last, best hope" to "save America" is mainly interested in serving Israel and banking and corporate interests, not the American People, who once again are being played as Heritage America continues to quickly become part of the dustbin of history. At any rate, what I experienced as a proponent of a pro-White, pro-American political party that was for a while the fourth largest political party in the country after the Republicrats and Libertarians is ancient history now so I'll try to to a better job of not expressing how angry and frustrated I am at seeing us go down "in real time" as the expression goes.