The Republicans and Democrats make the rules and rig the game. This allows them to continue to do the “stellar” job they have done and reward each other by voting in in their own raises, own pension plans and make sure they not be bound by the pesky rules the rest of us must regarding things like insider trading laws.
Anyone who manages to serve 5 years in the House is set for life with at least a modest lifestyle. A third party candidate with any oratory skill could anger enough of the sheep to really cause some problems. The trough is too full and, both sides too dirty to let this happen.