Fair warning; this is going to honk off a lot of my fellow old-school gamers.
I play AD&D. That's 1E to all you johnnies-come-lately with your fancy "editions".
I've got a group of players who have been playing this version of the game for more than a year and a half now. Only one had ever played before, and had long since moved on to newer versions. I've never asked, but I assume it was the same reason most people move from one version to the next. Not that it's necessarily "better" (although TSR/WotC is certainly within their commercial rights to try to convince its customers of that), or merely because it's the latest thing (is there an antonym of atavism?), but ultimately because it's the version that is "currently supported."
I think a lot of gamers fall into this trap. They refuse to play a game that is not being "supported" by a publisher. No more PH, DMG, or MM. No more modules or campaign settings. No magazine articles. It's almost as if a lack of new "official" material renders a game somehow obsolete.
I find that a quite remarkable attitude, and one that runs counter to any sort of common sense. Yet it is at the heart of the entire "retro clone" movement. Games like OSRIC, Basic Fantasy, Labyrinth Lord, Encounter Critical, etc. Each and every one of them is no doubt fine in and of themselves, but I must wonder at why they exist in the first place.
Who says to themselves, "I think I'll run an OSRIC game"? (And I don't mean to pick on OSRIC in particular; it happens to be the first one that came to mind; these points can be made relating to all of the retro-clones, inversely proportional to how much they stray from the game they purport to be a clone of.) Given the choice, why not just run an AD&D game?
In OSRIC's case, it was conceived as a way to allow publishers to put out AD&D-compatible material. But, of course, that is completely unnecessary. Mayfair Games was putting out AD&D-compatible material for years. More recently, Pied Piper Publishing has come out with adventure modules which are completely AD&D-compatible, and did so without the need for OSRIC. You don't need OSRIC to play AD&D, you just need, well, AD&D.
Is it the case that the rulebooks themselves are unavailable or prohibitively expensive? Certainly not, given both the after-sale and pdf markets. You can pick up a Player's Handbook for around $5 (which I should point out is cheaper than they were when they were first published!). I've got half a dozen myself, most of which I picked up within the last two or three years, for my players. The pdf versions, I am told, are similarly inexpensive. So, while "inexpensive" is certainly not the same as "free", in this case it's certainly not a show-stopper for anyone other than Barack Obama's brother.
It may perhaps be the fact that no new rules are being produced. This, as might be expected, is also a non-issue. Throughout the many years of Dragon magazine, literally thousands of rules suggestions, alternatives, expansions, etc. were published. With the advent of the Internet, thousands more have come on the scene. These are not "official" rules, I will grant. However, I would also point out that the game as originally published is complete as far as it goes. Anything else is gravy for the Dungeon Master, and "more rules" are hardly necessary to play. They are, however, amply available for the DM who wants to avail himself of them.
It is true, however, that many of the retro-clones are less clones and more new games in a retro style. In such cases, I can absolutely see wanting to try them out, and possibly even adapt them for the long term. However, I must wonder if any of them really needs to be a full-blown game. Could not the vaunted spider-goat have appeared in an unofficial supplement for Gamma World or Metamorphosis: Alpha? Could not some of the rules adaptations of Labyrinth Lord have been published as a series of optional rules for the Basic/Expert rules?
I suppose it comes down to the fundamental question. Do we need games to be "currently supproted" in order to play them? I tend to think not. Are there reasons I've missed? I'm genuinely curious.