There's this ongoing argument about how, in order for the Hero's Journey to be effective, the Hero has to come back in the end. No matter how good a time s/he's having, it doesn't mean a thing if they don't deliver the goods back to their own world.
This runs exactly at odds with urban fantasy's usual core theme: our secret world brings all the champions to the yard, and damn right, it's better than yours.
We saw it with Richard, who at the end of his journey returned to his own world only to walk through a door to Elsewhere. We've seen it with Rachel "More Magic Is Okay Magic As Long As I Pay It All Back Eventually, Right, Guys? ... Guys...?" Morgan. In a lot of ways, the offer the fantasy world makes is a pretty convincing one. It can provide intrigue, novelty, danger cloaked in beautiful guises. More often than not, the protagonist is needed there--special in ways that they, perhaps, aren't in their own lives. It's a gorgeous temptation. No surprise that protagonist after protagonist sinks deeper into the magic until they eventually find their lives populated with elves and werewolves and not a single human or brick house in sight. It's an understandable answer to a temptation no small chunk of the population would probably jump if they had the chance.
But a better question is: why must they choose at all?
In regular fantasies, the answer would be pretty obvious: nobody can live with one foot in Narnia and one foot in the real world. (They have names for people trapped in closets. Possibly medical terms, too.) But we're talking about urban fantasy. The point of the genre is the mingling of worlds--the blurring of the real with the fantastic. So why not invite the adults into Narnia? They're halfway there as it is. Why does the secret world have to stay secret?