In some cases, it takes only a single Congressman to prevent a law from being passed. If the minority party is dead set a bill -- if only for political reasons -- it often requires absolute unanimity on the other party to pass it, an unreasonably high bar to pass.
Legislation is nearly always trivial. They are only barely capable of passing even the most basic, crucial, mandatory law appropriating funds for the executive branch -- and that's only possible because the filibuster does not apply to appropriations bills. Real legislation is sometimes bundled into appropriations bills precisely to piggyback on that exception.
Theoretically, the legislature can do lots of stuff. Pragmatically, you can't simply say "well, the legislature should act". There is an enormous thumb on the scale in favor of the status quo.