I feel like RC D&D is the "forgotten edition", and I'd separate it from BECMI (I am aware that it is very closely related, kinda a compilation, but bear with me).
I think it's the "forgotten edition" for a few reasons:
1) It came out in 1991. So not that long after 2E. And at that time, I think most (definitely not all) people who played BECMI had either switched to 1E or 2E, were playing one of the massive array of new RPGs that had exploded out in the late '80s and '90-'91 (including Vampire, CP2020, Shadowrun, and so on) or had stopped playing (because they were at college, started work, or the like).
2) People who learned of it, tended to dismiss it. I saw this a lot on the early internet. "Oh that's just D&D, not AD&D, not interested!". At the time, being a teenager, I sorta believed this, but also having read RC D&D, I was sorta-super-impressed by it. Most people hadn't even read it, though, it seemed. More grog-y players tend to role their eyes at it for similar reasons.
3) It wasn't presented by TSR as an introduction to D&D. It didn't really have a clear purpose. I mean, in a sense it's classic TSR "competing with their own products" stuff. If you were an AD&D player, why would you buy it? If you were new to D&D/RPGs, there were other products for that, and it wasn't really linked to them.
As a result of all this, I think you have this small number of RC D&D evangelists, who have read it, and were really impressed by it, because, frankly it was accidentally way ahead of it's time design-wise, and a large number of people who just have never heard of it, or think of it simply as a compilation book for BECMI that's not really it's own thing (even though I would argue it was). And younger players tend to be aware that there's 1E-5E, and that there was "red box" D&D and sometimes that there was OD&D, but they are rarely aware of RC D&D at all, let alone of how well put-together it was.