According to Janus, one factor in determining whether a prior decision should be overruled is that is was "poorly reasoned." I'm tempted to make that the sole "explanation" of this post's title, but to be clear about the point: Romer and Obergefell fit that description (in my view, Lawrence doesn't). The headnote to Janus offers a crisp summary of another factor (the opinion is less crisp, but the headnote is accurate): attempting to salvage a weak precedent by recasting its reasoning. From the perspective of its critics, that describes Roe v. Wade in light of Casey.