Neither is seen in stores because these two probably have the highest percentage of shooters that load their own than any cartridge. With stash prices I can load .357 for less than $0.15 per round. The only .357 in stock at SGAmmo is $1.28 per round. Consider a hard to find Coonan or a couple of others are the only auto .357's (newbies only want autos) made and you can see why the .38 and .357 are dying. I have a few of them so don't blame me. Aside from cowboy stuff the .45 Colt is going away too. When was the last time you saw .44 magnum on the shelf?
It takes a very long time for a cartridge to die all the way though. Just look at the .32-20 WIN. It's a black powder era loading and it still has a small following as seen below...