I don't think it has much to do with judges turning more liberal over the course of their career or trying to act in a way to get to the court and then easing up on their stances when they make it, at least not in these particular cases.
It seems more like there are some specific issues that judges care about. Well, at least some of them. Alito and Thomas are lost causes, they have pushed through basically every Republican agenda regardless of how stupid and / or unconstitutional it is, twisting themselves into pretzels while doing so. But the others all have their specific points they care about. Gorsuch has the rights of native americans as a topic, while Kavanaugh has state rights. Just look at the current decisions. He voted against the change in Wisconsin, because the decision came from a federal judge and thus didn't come from the state, and then he upheld the decisions in North Carolina and Pennsylvania, because those were made internally by the state. Roberts doesn't really have one specific issue, but you could make the case that he doesn't want his legacy to be an absurdly partisan Supreme Court that just let the Trump administration run wild. He's definately still very much a conservative, but unlike Alito and Thomas, he does have scruples.
It seems more like there are some specific issues that judges care about. Well, at least some of them. Alito and Thomas are lost causes, they have pushed through basically every Republican agenda regardless of how stupid and / or unconstitutional it is, twisting themselves into pretzels while doing so. But the others all have their specific points they care about. Gorsuch has the rights of native americans as a topic, while Kavanaugh has state rights. Just look at the current decisions. He voted against the change in Wisconsin, because the decision came from a federal judge and thus didn't come from the state, and then he upheld the decisions in North Carolina and Pennsylvania, because those were made internally by the state. Roberts doesn't really have one specific issue, but you could make the case that he doesn't want his legacy to be an absurdly partisan Supreme Court that just let the Trump administration run wild. He's definately still very much a conservative, but unlike Alito and Thomas, he does have scruples.