Usually, off-exhibit holding areas are more-so function over aesthetic, guests aren't often going to be looking at the quarters (unless viewing is obviously provided), and some off-exhibit enclosures may be accustomed to whatever fits the animals' needs (ex. birthing, new arrivals, veterinary reasons, etc.). If it's however for rehabilitation or rewilding purposes, enclosures will often be similar to their natural habitats to allow animals to prepare for whatever's out in the wild.
Some of the general public seems to get a false notion that an animal is being "abused" simply because the areas often don't look naturalistic; thing is, the animals aren't going to care as long as their needs are satisfied. On many social media accounts that pertain to posts of animals in these areas, there is always that chance that someone is going to complain about "subpar" living conditions when in fact, it's just part of the area in itself. Some animals even prefer hanging out in off-exhibit areas over being on display.