Because Supreme Court cant create their own laws directly, missing legislature power, having no direct power to control national finances/budgets, a main power of a country and they dont have control of the executives including army and police. All their power depends on laws made by legislature and constitution.
Thats how the three pillars of power works in all democracies. Just because your legislature or executives or even forefathers who made the constitution fucked up, doesnt mean the supreme court is an absolute monarchy. The biggest piece of shit mistake you made was having a two party system. In other countries, supreme courts arent as binary partisan. Coalitions of Partys vote way more reasonable judges to supreme courts