From a military perspective and from a social perspective, why was attrition allowed? Were people back home simply not aware of the high casualty rates until after the war? Did military commanders believe this was the only way to victory? Or, did they genuinely not care about their men?
Hi, I've written quite extensively about this topic. Some of these AH posts may help you:
On the "Lions led by Donkeys" myth
Our very own NMW put it best though in this post "In World War I, why would a General ever order his men to attack an enemy trench? Why not sit back on perpetual defense, eventually having millions of extra men due to an excellent casualty ratio?" why these things were done. This is probably the most concise dealing with attrition rates I've seen.
However, I must also recommend a cross-post to /r/badhistory in a more lengthy (but warning much more abraisive) post I made about general WWI myths but more focused on attrition, 'human wave tactics', dumb generals, etc: "Why did they bother attacking? Were the Generals a bunch of idiots? The issue with "human wave assaults". Who's this Haig guy and why am I hearing about his butcher shop all the time? A general dealing and reference guide to bad WWI military history.". If you don't mind the vitriolic language (was a bit of a catharsis for me) I'd say this is actually a great place to start for some of these answers as well.
Here is one I made earlier, from which this feels relevant
No, the casualty rates were not remarkable. The absolute numbers appear shocking because for the first time in history it was possible to maintain an army of a million men in the field indefinitely. The high casualty lists are simply a function of the sheer scale of operations and the vast numbers involved - The Germans may have lost 40,000 men on the first day of the 1918 Spring offensive but they attacked with 74 divisions. That's more divisions that they had in the whole of western Europe in 1944