And it wasn't even their marriage at stake.
If someone is daft enough to question whether or not the issues of marriage, divorce, annulment, and the Church's views on these subjects are important, recall that these two men were martyred essentially for defending the Church precisely on these topics. If the Church's jurisdiction over marriage is really something dispensable or if first marriages really don't matter (as Cardinal Kasper suggests), then both saints died for nothing.
Of course, we tend to forget what all martyrs died for because a lot of it is stuff that many of us Catholics do on a regular basis anyway. Not being able to take the cognitive dissonance, we write it off to "dying for Christ" so that we aren't faced with "died to convert pagans to Christ," "died to defend Christ's Truth against heretics," "died for refusing to commit sacrilege against Christ by attending schismatic liturgies," and so forth.