Easy, because the main Make just does a
for i in $SUBDIRS; do $MAKE -C $$i; done
which cannot be parallelized unless you somehow propagate the -j into the
submake, which standard GNU make cannot do because it doesn't have a
central "how many jobs are currently running" counter.
Adding such a thing is basically impossible, unfortunately, unless you want
to reimplement a /bin/sh parser inside Make. :-/
-- Matthias Urlichs noris network GmbH- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu