The (rnrs (6)) library is intended as a convenient import for libraries where fine control over imported bindings is not necessary or desirable. The (rnrs (6)) library exports all bindings for expand as well as run so that it is convenient for writing syntax-case macros as well as run-time code.
The (rnrs (6)) library does not include a few select libraries:
(rnrs eval (6)), as its presence may make creating self-contained programs more difficult;
(rnrs mutable-pairs (6)), as its absence from a program may enable compiler optimizations, and as mutable pairs might be deprecated in the future;
(rnrs mutable-strings (6)), for similar reasons as for (rnrs mutable-pairs (6));
(rnrs r5rs (6)), as its use is deprecated.