Why is case life important? Why not? It is important to some shooters, not important to others.
One of the advantages that sharper shouldered cartridges have over sloping cases is their extended case life. You can see this especially with Ai cartridges- they last quite a long time, and yes- it is important to more than just target shooters. For instance, AI users need to fireform cases- Do they want thier cases to only last 2-3 firings?
You may not have been convinced that cartride geometry affects life, but I have. Loading for cartridges like the 375 H&H, 303, 30-30, 22-250 compared to cartridges like 338 WM, 30-06, 308, 22-250 AI, I've seen a big difference in case life, and no, it's not just the rifle.
If you haven't observed different case life based on cartridge shape, you probably haven't loaded for a wide enough variety of cartridges.
I like to shoot alot. My 375 H&H went with me to every range session, as will the 375 Ruger. I liek to keep in practice wiht a rifle that may be used on dangerous game.
You may only shoot your 375 every know and then, so 2-3 firings may be fine for you, but I will shoot mine alot. I don't want to be ordering cases every other week.
Of course not. I purchased it because it gives me exactly what I would want.
When I sold my 375 H&H Brno 602 (also owned by Supercub) I knew I wanted another 375 with similar performance. Based on that rifle (generous chamber) and another 375 H&h I had loaded for (tight chamber)I knew I didn't necessarily want another H&H. It is a great cartridlge, but case life bothered me.
I initially looked at the 375 Weatherby, 375 AI and 375-338, and even bought a rifle to build one of these on. it would have been stainless, synthetic, CRF action, 20-21" barrel, sturdy iron sights and ready for a scope, too. Then the Ruger came out, (in the African model) and I was going to build a 375 Ruger, by my specs, as it seemed to be more practical than the other choices. And then the stainless Alaskan came out, and it had what i wanted- 375 H&H + performance in a much more compact, stainless package. Had Ruger offered the same rifle, chambered in 375-338, 375 Weatherby or 375 newton

I would still have purchased it.
Unless you have creeped up coastal spawning channels, seeing dinner plate size grizzly tracks, freshly chewed salmon carcasses, and tried to quickly swing a long barrel around in thick cover, where a grizzly could be 30 feet away and you would not be able to see it- You probably would not understand the attraction to the 375 Ruger Alaskan.