well the lore of warcraft which you seem to take very seriously is a little ridiculous, isn't it?
i kinda doubt that after what happened to the elves they care about Garithos' emotional state, or about whether it was Arthas himself or the whispers of the frostmourne or whatever
what they did care about is results: their homeland is destroyed, their people slaughtered and their allies failed to be of any use, to make matters worst instead of at least providing some form of aid even after the invasion (to help them rebuild)- or at the absolute rock bottom to make some sympathetic statement with empty promises, they don't even intend to keep!-they manage to get even lower than that: the alliance is openly insulting their leader with racist remarks about 'pointy ears' (ridiculous writing for sure but it happened nonetheless) and is not above in using the survivors for military purposes
in my above ridiculous example is like NATO(alliance) saying: ok we get it you lost like 90% of your population, but you'll still send troops to assist us in Iraq, right?
and the elves actually do, and what does the alliance does? it sends them on suicide missions and brands them traitors
the alliance even goes as far as attempting to execute a foreign faction leader?! that's beyond ridiculous, i have no words to describe it
and here i have you, saying that they shoud remain loyal to the alliance...
ffs man, let's just accept it's a game, games are meant to be absurd, better not to think about it too hard