In general terms, there are legal benefits for the spouses and children of prisoners who are not the subject of the punishment, and should not be adversely affected for something they have not done.
In terms of 'celebrity' murderers with no chance of parole, the attraction is obviously not based on the standard relationship factors that lead to marriage.
I believe there is a powerful attraction for some inadequate women who struggle to form and maintain relationships, to be linked to a man with whom their relationship can be conducted largely on their terms.
They know exactly where he is every second of the day and night, he cannot cheat on them, run away from them, or create a similar bond with any other woman.
In order for a man to be in that position, he has to have committed a crime deemed serious enough that he will never be released, but for some women, his personal history makes the security of their relationship worth accepting what he has done.
Since, by definition, these women are not conducting anything approaching a normal relationship, it should be relatively easy for them to believe their fixation's protestations of innocence, and see him as a heroic figure cheated of his liberty by a cruel society that has treated him badly, probably in much the same way as they see themselves, as outsiders and victims.
But I could not agree that the sins of the few, like Belfield, should be used to punish the few more, with innocent people being affected by such a draconian measure.