Both current multicore GCs do exactly that to keep allocation cheap but there are different design choices within the constraints we could have gone with. To a

Both current multicore GCs do exactly that to keep allocation cheap but there are different design choices within the constraints we could have gone with. To avoid frequent synchronisation we could have gone with a (potentially generational) non-moving collector for the minor GC which would still have preserved the C API, probably allowed for very low pauses but would have made allocation more expensive.