Why the dearth of 'other world' campaigns?

JRR Tolkien was a crucial 'break' between two conceptions of the fantasy genre. Before him, most (though not all) fantastical tales either involved people in the real world, 'our' world, travelling to other realities, or situations in which the real world was merged with such other realities. After him, fantasy worlds took on independent existences: they were largely complete, enclosed creations - worlds in their own right, with no necessary connection to our own.

This was the major influence exerted by JRR Tolkien over D&D, and most subsequent fantasy role playing games. D&D does not involve adventurers from our world straying into others. Its campaign settings - whether official ones or the amateur creations of DMs - are discrete, and the PCs are 'native' to them. And this is true even of multiworld or multiplanar settings like Spelljammer or Planescape; the PCs in such settings are from the broad canvas setting as such, rather than our own.

When I was young, I much preferred this state of affairs - I thought fantasy fiction in which an 'ordinary boy' (or whatever) from 29 Acacia Avenue accidentally wanders into Dragonland were the absolute pits. As I've got older, I've come to understand the appeal. And it has come to mystify me as to why nobody has ever really successfully 'OSRized' a particular concept which makes complete sense when you think about the history of fantasy fiction - a campaign archetype in which people from the real world go adventuring in a realm of fantasy and thereby gain improvements and advantages which they can deploy when they come back. No doubt such games have existed in the history of RPGs, but I have not heard of one that has sounded remotely interesting - and certainly not in recent years. 

The Chronicles of Narnia are the obvious model for this: the PCs are ordinary children who gain access to portals to another world where they have adventures, and as a result of having these adventures, their real lives become powerfully enriched when they return. Another example would be Stephen Lawhead's Song of Albion series, an (excellent, by the way) series in which an American academic accidentally strays into a mythologised bronze age Britain and comes back transformed into a muscle-bound nobleman irresistible to women - wish fulfilment, of course, but charming wish fulfilment for all that. Slightly different is the Chronicles of Amber, wherein an ostensibly 'normal' man discovers he is actually a demigod and that there is an infinite other reality out there for him to explore. And then, of course, there's Mythago Wood and its sequels, in which Big Important Things happen to people in the wood, and they come out forever changed.

The archetypal iteration of such a campaign would I suppose be the one in which real world people discover a portal to another realm (the Abyss, Valinor, Middle Earth, whatever), amass treasure and magic, and bring it back to sell and gain power. Kind of like what I was planning with There is Therefore a Strange Land, come to think of it... With the right kind of systematisation for gaining XP and level advancement, and a compelling setting - I think it is important for such a campaign setting to succeed that the PCs are part of a secret subculture - this could be an important addition to the OSR canon.