It has been designed this way since the 60's after they intentionally left out other candidates in debates, belittling them as third-parties, and pushing this separation politics narrative into a severely corrupt two party system. I could go on at great length and detail but I grow tired of repeating myself so much just to be ignored or ridiculed.
Succinctly, if you want to fix things, a good start is to reinstate the Fairness Doctrine, Glass-Steagel, and Dodd-Frank.