Another explanation is that Tolkien didn't want to complicate things for his initial audience, his own children. And since the Hobbit was meant to be read on that sort of level, with Wind In The Willows and the Pooh books, reality isn't required. In fact, it is a hindrance! If you look at all the kids movies where they go off and do wonderful things there is usually a lack of a mother that facilitates the story. Moms won't let you play ball in a sandlot, fearing you will fall down and hurt yourself. Dads, on the other hand, are more of the "Oh, you got shocked when you stuck a fork in a light socket? Bet you won't do that again" school of learning. So if you are going to go through strange wardrobes or play games that lead you to cavort with dinosaurs or talking animals, ask Dad. Mom won't let you make a sandwich by yourself.
II have my own theory, of course, and it is quite simple and straightforward. Tolkien's Father died when he was only 4 and his Mother when he was 12. His Guardian was Father Francis Morgan, and he was raised a strict Catholic. This caused some difficulties when, at age 16, he began courting an older woman, Edith Bratt, who was not Catholic. He was forbidden to see or write her until he was 21, and apparently he did so. Many things happened for Tolkien. He eventually married Edith, went to war and nearly died in the trenches, and various Professorships. He always found time to write, even during war-
. . .. in huts full of blasphemy and smut, or by candle light in bell-tents, even some down in dugouts under shell fire.
He settled down to family life, something very important to him. He remained a strong Christian, and his family values stemmed from his faith. It is my idea that he not only made Bilbo and Frodo bachelors to make the story simple for readers and to avoid any unnecessary plot sidelines but because to his way of thinking it was unethical for a family man to abandon his wife and children for something so shallow and pointless as a treasure hunt with Dwarves. Frodo, maybe- after all, he would be protecting his family in the long run- but why complicate matters? If it was foretold for Frodo to undertake the mission- and Tolkien has Gandalf drop strong hints that he was- then he would never have felt right about marriage, knowing in his heart of hearts that he was fated for something else.
Bilbo being single was right, not only for good plot structure but for his sense of family and social interactions. Men that ran off for adventure were irresponsible losers, not heroes. If there was one thing Tolkien believed in it was family! All through Lord Of The Rings there are many examples of this, and finding a character that wasn't married was either because they were widowed or because a future wedding was part of the plot, as in Aragorn and Arwen, Faramir and Eowyn. Or even Sam!
The Hobbit started out with a peculiar bachelor living his own little private life in his luxurious Hobbit Hole, all by himself. Bilbo wasn't a hermit, by any stretch! He loved social events and having guests, but preferred to invite them himself, not have 13 strangers drop in! But alone he remained, until he invited another Baggins, Frodo, to live with him as his adoptive heir. But the story ends with Samwise Gamgee, who finally gets up the nerve to ask Rose Cotton to marry him, coming back from the Grey Havens, having seen Gandalf, Elrond, Frodo and Bilbo depart for ever to the Undying Lands- bachelors all, excepting Elrond, and his wife had already sailed over the sea after experiencing harrowing ordeals, having been captured by orcs. So Sam rides back to the Shire, enters Bag End- now his, Frodo having made Sam his heir- and places his little baby, Eleanor, on his lap and says, "I'm back." And that is how it ends. Very appropriate for the orphan that found so much in his family and adored his wife.
Tolkien only outlived Edith for a couple of years. This headstone reflects how he thought of her, as the legend of Luthien and Beren was a very early story that involved a mortal man, Beren, and his love for one of the most treasured of Elf Maidens, Luthien, and the trials they had to go through to be together. If ever there was a life-long love story, this is it! And, yes, Tolkien would have left his beloved Edith and family to save them and the world, but most assuredly not for a simple treasure hunt.
