It takes only four votes to grant review, and, according to this theory, if the three more right-leaning justices (Samuel A. Alito Jr., Antonin Scalia and Clarence Thomas) were ready to consider those cases, they apparently lacked Chief Justice Roberts’s vote. But these votes are done in secret, so one can only speculate.
Putting aside previous cases and previous votes, there are a number of institutional reasons Chief Justice Roberts might, and should, cast a vote for the freedom to marry.
First, a Supreme Court ruling authorizing the states to restrict marriage to heterosexual couples would lead to enormous confusion. The court’s decision not to take appeals of earlier cases, or put other appeals of lower court decisions on hold, has induced many couples to marry. Surely, same-sex couples who married when marriage was legal under prior court rulings would remain so. But if the plaintiffs do not prevail, all of the states that recognize the right of same-sex couples to marry in light of lower federal court rulings could revert to their earlier state of affairs.