As social norms change, the laws that guide critical decisions change as well. Grandparents' rights were legally non-existent in most places just a few decades ago. With the increasing risk of the opioid epidemic and other familial issues giving rise to grandparents raising their grandchildren, more grandparents are eager to protect their relationship with their grandchildren through legal means.
When married couples with children divorce, they have their previous relationship to look back on when plotting their new co-parenting roles. While that can be both good and bad, it, at least, provides a familiar framework upon which a co-parenting relationship can be built.