Notice how in action films they often contain a lone protagonist whose partner recently died, or was killed off, often as a reason for starting the plot. Even Disney films do away often with the parents which I argue holds the same emotional position as a spouse in stories.

As a writer it's hard to write action and adventure stories with the main protagonist having ties to a parent or spouse. I'm not saying it can't be done, but it's much harder and I assume many writers forgo the spouse/parent all together to make the story easier to write.

It's hard for a writer to write a story that involves someone going off on a difficult, life threatening adventure while they have a spouse. Imagine if you were going off to fight evil monsters or men, how would your spouse react to that? "You want to do what? And kill what? We need you here with the family not out getting killed!"

Including a spouse or parent forces the writer to deal with the mundane aspects of those relationships which often clash with high adventure. If you read Greek mythology you will see the complications spouses cause to stories. Of course in those days men did what men do and women just had to suck it up if their man went out into the world to fight demons for the next seven years, all the while she sits at home, celibate and wondering if her mate was still alive.

With modern ideals of relationships, that can be a hard thing to include in a story while still trying to make it an adventure. I would think stories that contained spouses would have to revolve around the relationship or focus on the pair as a team. Spouses bring complications to stories and often the writer wants the complications to be about things other than the relationship so do away with it altogether.