If leadership-aligned politicians won't dare step out of line, and those opposed are systematically marginalized by the executive, other legislators, and the courts, then what good does that do? Deliberately neutralizing the opposition's power renders the opposition's ideas, efforts, and proposals useless, and the allied politicians will never disobey, so petitioning either of them to make changes is pointless.
I'm not saying any of that is completely true right now, but people are nervous that this is becoming true.