Well, that model does seem to generate a tidy income, so I imagine that it will continue until it does not.
I suspect that the "bigger epic storyline" is successful because the public likes it that way. Franchises and shared universes breed familiarity, familiarity breeds trust, and trust increases sales. It's literally branding, baked in to the product itself. Conversely, standalone films of any kind that aren't related to any established property confuse moviegoers and terrify the executives who write the checks. That's why expensive movies are virtually always associated with another movie, book, TV show, play, event, board game, or theme park ride. Anything that the prospective moviegoer will recognize, and feel comfortable buying tickets for.