Why not indeed?
One of the reasons there are so many more bullets over 250 grains available for 9.3's is that for a long, long time the standard rate of twist for .35's was 1-16, which won't reliably stabilize spitzers over 250 grains.
But if a .35 has a faster twist (and my own .358 Norma has a 1-14) then heavier bullets can certainly be used. Mine shoots well with both the 280-grain Swift A-Frame and 310-grain Woodleigh.
The other answer, of course, is that, like Mount Everest, the 9.3's are there.
