Campaigning in the US relies heavily on money from wealthy investors to get off the ground. Meaning, any new party that wants to get going needs approval from the wealthy to do so.

Additionally, a huge percentage of the population pays no attention to politics at all, just closing their eyes to the whole election and either not voting, or voting for the party they've always voted for every time, so even if your party managed to get some attention, it'd just be another 3rd party further fracturing what small portion of the population risks voting outside the 2 party system as it is.

In other to have a shot at winning, you'd need to somehow make enough money to afford competing with the 2 established parties for screen time, which would mean major corporate backing that would only happen if they liked your policies.