IANAL but most contested Supreme Court decisions I've read (going all the way back to AP gov class) sounded like they could have reasonably been decided either way depending on who had control over the court. The law is ambiguous and complex enough that there's just so many logical ways to approach a decision and little in the way of prioritizing or disambiguating them. Whatever their bias, judges have lots of ways of reasoning themselves to their predetermined outcome. This is true up and down the courts but most judges are at least somewhat worried about their reputation and their record with appeals courts, which at least mitigates their biases but the SCOTUS is free to do whatever it wants.

As much as each side likes to bloviate about originalism and activist judges, SCOTUS often decides at the whims of ideology and personal bias because the law gives them lots of room.