Germany is based on the experience of the Nazi's raise to power, one thing Germany got right after WW2 was the German constitution. Stuff like the 5% hurdle to get seats in parliament for example. The US on the other hand still seem to struggle with a system put in place after the civil war to suppress the black vote and satisfy the former confederate states. But I might be wrong.
No need to present your ID to vote, your invitation is enough. Your ID will do if you forgot that invitation.
So in a sense, we have. A mandatory, government run. You cannot be purged, we don't sign ballots (our elections have to be 100% anonymous), we don't need our ID to vote. And any party affiliation is not part of that system. makes stuff a lot easier, and individual parties cannot toy around with it.
This is sort of a dumb idea, really. But it's not as broken as you imagine.
So democrats would oppose a Green or other progressive candidate in (most races in) New York, sure. That's just self-interest. But for the same reason they'd clearly welcome a libertarian entrant. That's not responsive to the discussion.
The claim upthread was that "both" parties oppose ranked choice voting. And that's simply not true.
A single party's goal may be to avoid direct competition but they work together with each other to prevent all other parties. This is one of the things that's easy for them to have bipartisan agreements on.
To get a candidate on a statewide ballot you have to get signatures from a percentage of registered voters. I don't remember the numbers off hand but it's in the tens of thousands. This alone is both cost and time prohibitive. There are also a bunch of other hoops you have to jump through.