IMO, I'd actually like to think that, like picklepikkl linked and quoted the Picard quote, the Mors alt "game" is characterized by: "It is possible to commit no mistakes, and still lose. That is not a weakness. That is life."
They simply... did not have the ability to receive intel reports on what was going on in the surface. Because they're literally cut off from the surface.
*Citadel entrance to overland: blocked by giant spiders and then Dwarfs
*Karagril: Dwarfs
*Zilfin: Skryre and Motherfucking Dragon
*Yar: Eshin all the way.
*Rhyn: Greenskins
*Mhonar: Seriously, Fuck This Place, It Just Kills Our Dudes Dead And We Still Have No Idea What It Is
*Kvinn-Wyr: Trolls. Also, not actually available to them -- it's on the other side of the Under-Citadel.
They literally don't have any major routes open to the surface. It's guesswork as to assume whether or not they have secret special Skaven tunnels that can do so.
Which means that their level of knowledge would consist of: "Citadel changes hands from Greenskins to Dwarfs; then giant spiders rolled into the Under-Citadel and set up shop there." "Karagril was assaulted by Dwarfs, and a surge of Karak Drazh Orcs -- we can assume the Dwarfs have come to Karak Eight Peaks, may hold a peak or two." "There were multiple throngs involved; Karak Azul, and Clan Angrund. The Clan of K8P. And a bunch of human mercenaries." (Note: they may not actually have enough knowledge to be able to recognize Karak Azul, or differentiate it from Belegar's Throng.) "Dwarfs have set up defenses in Upper-Karagril; they are not aggressing against us, however."
So what does the situation look like for Clan Mors? For their awareness?
They might not even know about any Wizards in K8P. They might have
assumed that, with the presence of lots of human mercenaries, the humans might have brought a wizard or two. But that's just extrapolation on their parts.
They don't even know that somebody assassinated the Karagril Orc leadership. They just know that the Orcs collapsed into infighting one day, with several bosses dying, and that the Karak Drazh orcs started streaming through the Underway.
They know that Dwarfs are in the Citadel, and in Karagril. They know that the Dwarfs obviously must have set up defenses against Under-Citadel (because there's giant goddamn spiders there) and in Under-Karagril (this time, they saw this personally).
They know that the Dwarfs brought human mercenaries. They know that there are thousands, maybe several ten thousand, Dwarfs.
They know that the Dwarfs have not aggressed against them in all this time. At all. They fortified Upper-Karagril, and then did not attack them at all.
And that's... probably all.
Them blaming raids and theft on Clan Eshin? That's totally reasonable of them.
So... As far as Clan Mors was aware, the Dwarfs only even have access to them via Karagril... and they're not budging from there.
When their GM throws this Turn Of Horrible Surprises at them, I like to think that he is more likely to give the Picard quote than the "You were metagaming
" comedy sketch. The players did not know what they were dealing with... But then, they simply were not expected to be able to know it, due to their limits.
It's just sad all around. They were in dire straights. They were making the best choices they could. Playing the best they could. They even had some strategies and means for possibly surviving or winning; mostly by being prepared, and waiting for an opportune moment -- like the Karagril assault. And now the Eshin assault.
And then, despite them doing their best, they got served a raw deal anyway.