The former want the language to stay as minimal as possible with a tiny standard library so that there are fewer concepts and options for students to stumble over. The latter want a full-featured language (but still minimal, it is Scheme after all) with a large standard library of useful types and functions so they can get stuff done.
These two perspectives are both reasonable but fairly incompatible.
For most of its history, Scheme leaned towards education. Around the type of the sixth edition (RSR6), pulled somewhat the other way and the language and library spec got much bigger. This alienated a lot of folks who wanted to stay a small teaching language.
For RSR7, they tried to resolve that by simply splitting the language in two: a small one and a large one. Then each subcommunity can have what they want.
Around the same time, the language PLTScheme renamed itself to Racket to clarify that they aren't trying to be beholden to the overall direction of the Scheme community. Racket is also a "large Scheme" in that it's a Scheme-derived language that tries really hard to be batteries included for all sorts of uses. It also can be "subset" into smaller languages for use in teaching.
My impression (from far on the outside) is that Racket has taken up a lot of the oxygen, which may partially explain why RSR7-large never managed to reach consensus and ship.