I'll just disagree because I think your statement is highly inaccurate.
Regarding who gets on the ballot - yes there are a special interests that fund their candidate. We generally get whomever has a larger budget, not who the best candidate might be. Special interests also drive the ballot measures too.
> In the US the parties don't really exist, there are just people.
This makes no sense. Just recently (2016) the Dems showed clear bias against Bernie in the leaks. The Chair resigned. The party always has a platform, a brand, an agenda and big budgets. Also third parties have almost zero shot because the 2 major parties conspire to keep them out. It's not just "people". The Ds have their consistent supporters and the Rs have theirs. That includes corporations, special interest groups and more.
You have non-citizens driving these politicians. Big donors, some unions (like police), special interest groups. Health care, gun lobbyists, etc.
"Analyst James A. Thurber estimated that the actual number of working lobbyists was close to 100,000 and that the industry brings in $9 billion annually.[6] Wall Street spent a record $2 billion trying to influence the 2016 United States presidential election." [1]
"Who got special deals in the stimulus and why they got them. In the $2 trillion package, senators took care of their home state industries and pet projects." [2]
Casinos and airlines, among others, flexed their clout in that stimulus.
From the homepage today: "AP: Catholic Church lobbied for taxpayer funds, got $1.4B" [4]
Even more damning:
"We looked for legislation that was written by special interests. We found it in all 50 states. When legislators propose new laws, they don’t always write the bills themselves. Corporations, interest groups or their lobbyists often write fill-in-the-blank documents then shop them to state lawmakers."
"These copy-and-paste bills are commonly known as model legislation. More than 2,100 of these bills have been signed into law in the last eight years." [3]
[1] https://en.wikipedia.org/wiki/Lobbying_in_the_United_States
[2] https://www.politico.com/news/2020/03/26/stimulus-coronaviru...
[3] https://www.usatoday.com/pages/interactives/asbestos-sharia-...
[4] https://apnews.com/dab8261c68c93f24c0bfc1876518b3f6