Rights are won through struggle
The Left has failed to succeed in America in part because it treats the law as though it should remain sympathetic to our causes even when we do little or nothing to protect them.
According to Karl Marx, "between equal rights force decides." The Right has continued to win because, over the long term, they have chosen to use force far more than the Left. Meanwhile, the Left typically refuses to accept that pacifism is a position of privilege, and that total opposition to the use of force leaves the law highly vulnerable to repeal.