First thing to note:
S30V is usually heat treated to Rc 57-59 range, and sometimes in the Rc 59-60 range. That is how hard the steel is and can affect edge holding and wear resistance.
M4 is somewhere in the Rc 63-65 range and is much harder than other steels. Stain resistance isn't that much higher than 1095 though.
M390 is said to have slightly better edge holding than M4, and is stainless on top of that. Hardness is said to be Rc 60-62, but I feel it's closer to Rc 60-61 unless it's custom heat treated.
1095 offers a level of toughness that most stainless steels simply aren't physically capable of. This is why you don't see stainless steels in any good katanas or swords. The ones that use them typically break easily and causes injuries because of it(if you haven't already seen that video). However, most stainless steels would be tough enough for much smaller fixed blade knives. Though you won't see 1095 used in swords either since the high carbon content would make it more brittle than something like 1060 with a lower carbon content. In a knife, it offers excellent toughness, hardness is typically Rc 58-60, and it's easy to sharpen without a lot of carbides.
I can't really say why Chris Reeve runs S30V so soft in his knives. Some say it's a cost saving measure. Some say it's to make it easier to sharpen. The more wear resistant a steel is, the harder it is to sharpen.
As for why Chris Reeve doesn't use a "better" steel... One reason might be domestic availability. Some makers want to support people at home, and so buy steels from the U.S. I believe that to be the case with Rick Hinderer as well. Another reason is that it would take time and money to figure out how to consistently heat treat a brand new steel type. And while it seems obvious that the "better" steel should be used, again more wear resistance means more difficulty sharpening.
Though my personal opinion is that someone should take a run of their flagship knives and offer a variation of it using "higher-end" materials, all the while keeping the regular version in production. I could see the Sebenza being much improved with a full-anodized finish on their titanium handles and CPM154 blade steel at Rc62.