Much like crypts and burial chambers, the frost caves are subject to random generation. So sometimes you get lucky and sometimes you don't. I once had a swamp crypt with a grand total of zero iron and about 3 yellow mushrooms. Each hallway at the entrance was just sealed off, no way forward. It happens. I've had frost caves that are pretty large with many cultist chambers, have scored upwards of 20-30 fenris hair. And I've had duds. Roll of the dice when you explore a new cave, just have to keep looking, I think. For good caves and silver for that matter, try the really big mountains. Smaller mountains are hit and miss. Big ones usually pay off.