I think it's because it's entry level. Let's be real, and I say this as a 1e fan, AD&D was not user friendly. There are clones of AD&D out there, but I don't think they have the appeal because b/x is much easier to learn and scratch that old school itch. Once people get in, and like it, then they go with things like Advanced OSE (which is AD&D).Just out of curiosity, why is B/X the (current) focus of the OSR community? Why not AD&D or 2E or BECMI? What makes B/X (and by extension OSE) the primary tool for folks dipping into Old School D&D?
There was a weird period where everyone pretended that OD&D was the epitome of game design.B/X isn't just the "current" focus of the OSR, it generally has been the focus through the whole thing.
I said "current" because I remember when it first started with OSRIC and that dominated initially.B/X isn't just the "current" focus of the OSR, it generally has been the focus through the whole thing.
I recall OSRIC being a curiosity, mostly, except for a few early adopters, and then the bandwagon getting rolling with Swords & Wizardry and Labyrinth Lord, along with many less-popular games. Although if you mark the OSR from starting with Castles & Crusades, we're back to 1E being the dominant mode again (IMO -- obviously there are people who'd call it a 2E game or its own thing entirely).I said "current" because I remember when it first started with OSRIC and that dominated initially.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.