could be map limitations, engine limitations, simply unfinished landscape and boundaries, no need to read too much into it.

I instead, if Scenario is reading want to suggest something that could be fun to have in the new landscape and help with immersion, without being too frustrating. It takes inspiration from the weather debuff in Forochel



Gnawing Cold - Lotro-Wiki.com


it can be trasposed in Umbar with something like Sand Storm: the whirling sand reduces your vision (applies an accuracy/evade debuff or reduces the draw distance)
and another like: Swelling Heat: the blazing sun hinders your resistance, seek the relief of shade to cool down.
This assuming it will be a desert-ish region but... food for thought anyway