The principal element in escapist fiction is difference. Not solely from each other, but from everyday life. Differences in lifestyle, in period, even in the world those characters inhabit.
Part of what makes Tolkein so engrossing is simply the detail of his world, so different from our own, yet drawing on such similarly-flavored societies. There is enough to get lost inside, which many have. Teasing out each detail, savouring its same-but-different peoples and lands, is probably why it has lasted so long.
His legions of imitators, on the other hand, simply perceive the plot: small-town halfling travels lots, does good, saves world. Which leads to hordes of trilogy (or more) based fantasy stories that at the very least involve a not-so-worldly individual traveling the world, and stopping some Ultimate Evil along the way. Sometimes they’ll swap out the halfling for a kitchen scullion or perhaps an orphan Boy (or Girl) of Destiny, but that’s garnish on a well-established meal plan.
These stories fall short due to their sameness. Though Dragonland-Whatever is different from your backyard, it’s just a bit too close the wasteland of Mordor. Its similarity to its progenitor is what diminishes its quality. Those stories in the epic-fantasy genre that have succeeded are usually because they understood that it was not the plot that was successful, but that element of difference.
Hmmm… this kind of drifted into a Tolkein case-study, didn’t it?
To drift back: the principal of escapist fiction is to escape. This is a perceptual escape, so defined as providing a different perception. A difference from the normal. Whether that’s a difference based on living a long time ago (sometimes even in places far, far away), in places that never were, or even just playing poker with millions at stake, against a financier of international terrorism.
It’s not part of the world you’re living in. And the best sorts of escapism are often the most different.