Beside that 16K maybe not being enough, it's just a waste of resources. Most programs won't go out of memory, and if they do, dying while complaining about memory shortage is good enough. You really don't want to wast 16K (or whatever amount) for every process you are running.

The default should be what is best for most programs. And most programs won't have any code dealing with "out of memory" situation. Therefore wasting a chunck of memory is just, well, waste.