Protest voting doesn't work when the candidate you are protesting is the least worst option. Democrats that will not vote out of principle have been conned as badly as MAGA republicans. End of story.
I think you might be on to something. Maybe the system is set up to limit the power of protest voting? I mean, it does deliver two right-of-centre parties to power, over and over again.
Where the wheels are coming off is that one of them - and some people say both - are moving further rightwards, and this is destabilising society in America.
I think there may be some conflict in the interpretation of "set up". When you say it was "absolutely" set up that way, keep in mind that many if not most would interpret "set up" to definitively include intent.
Some people say… Dems are generally shit but they have definitely moved left over the last decade. A lot of new people have run and while it isn’t a sure thing by any stretch, people have been able to and have the chance to continue to move the party and also just straight up infiltrate it to push it left. Whereas the repubs have been in full sprint to the right.
Maybe the system is set up to limit the power of protest voting?
Not everything is some conspiracy to keep you down. The people who wrote the constitution just weren't perfect and had to make political compromises, which resulted in an imperfect system.
Also, the game theory that gives us insight into voting systems, telling us the current system leads to a 2 party system, did not exist when the US constitution was written.
The dynamic was understood, it just wasn't formalized in game theory terms. Alternative voting systems weren't in use though, and probably wouldn't even have been practical without automation.
Pretend you're a politician. You have two groups of people that want opposite things. One of them is reliable, donates and volunteers to help your campaign. The other is feckless and seems to always find an excuse to oppose you. Which would you try to please?
Young people don't get involved in the system and don't vote, nothing special about the US on that level, so it's not surprising their priorities aren't the priorities of the political options.