The underdark is lacking in certain resources, namely dragon hide and honey
now while i understand bees and caves dont do so well, our berries are supposed to be "larva" perhaps a similar "sweet goo" that is underdark appropriate could be added
now i know that not every resource should be found everywhere but the surface has access to every single resource, there are even scattered deposits of nitharit.
perhaps giving a low % chance for things like wyverns to drop hide, or adding a couple dragon bosses somewhere to drop hide to the UD can alleviate the issue, there is a dragon boss in the UD and it does not drop dragon hide.