Disruption in this vast market is difficult. Millenials and Xers will have to team up and work cooperatively. The baby boomers have gotten Democrats and Republicans to pander to them, there is no possible way those parties go away if baby boomers have any say about it.
As to why there are two parties, it's central to how the government is configured. No runoffs, range or preference voting, means that you get punished when voting for fringe candidates, because there's a very good chance the ideological opposite will win as a result of choosing a 3rd party candidate. Majoritarian democracies like the U.K. parliamentary system tend to have only two big parties, where consensual democracies like Switzerland and Germany have many parties represented in their legislatures. The U.S. is a hybrid, but the voting mechanism results in pretty much a two party system.
Do you have some examples of these types of laws?
The history of it is very interesting; essentially it was formed after the League of Women Voters, who used to run the debates, stopped running them because the system had become too corrupt: "the demands of the two campaign organizations would perpetrate a fraud on the American voter."
At a state level, election laws do things like guaranteeing the two parties a position on various ballots: city, county, state, federal. But then put in all kinds of onerous requirements for other parties just to get on the ballot. While Democrats and Republicans are using resources for other things, upstart parties have to spend money and volunteers just to get signatures in order to get on ballots and appear in debates. Primaries are tax payer funded, free publicity for established parties. Numerous laws exist for small things like elections commissions only having either Democrats or Republicans seated - i.e. if you're a third party, you can't even run for a state or county elections commission, it's prohibited. These sorts of things are very state by state or even by county.
But as I indicated in my original post, it's how U.S. elections favor the lesser of two evils strategy, else you get punished when voting for who you really want. Minor parties seldom get pluralities, and they suck away votes from an ideologically similar major party candidate which can cause them to lose, and then its the ideological opponent who wins as a result. Duverger's Law is what it's called.
For your second paragraph, do you have examples of the "onerous requirements"? Because looking at the ballotpedia list I don't see anything in there that is too onerous.
And again for your final paragraph, I agree that the system supports the lesser-of-two-evils way of thinking, but that isn't something instituted by Democrats or Republicans. It's built into the system at it's most fundamental level, the Constitution.