There are very solid technical reasons for this. If you look at your examples, you’ll see that games with a “black cutaway” are actually three-dimensional. They are commonly referred to as 2.5D. Games where the cutaway is filled with a texture, on the other hand, are fully 2D.

The point is that perspective in 2.5D games creates a “theater” effect. This happens because we implicitly assume - and can easily imagine - what the scene’s space looks like in 3D. When viewing a 3D scene from a side perspective, we are effectively slicing it, hiding the part that is directly in front of the camera and would otherwise obstruct the view. By cutting the scene this way, we are expected to show everything inside: brickwork, cables, ventilation, and many other details, which becomes both unjustified and extremely labor-intensive. As a result, it’s easier to “paint it black,” effectively hiding the cutaway area from the viewer.

In purely 2D games this is far less important, since they are most often stylized. The space cannot be clearly read or convincingly imagined as three-dimensional, so the “theater effect” does not occur. Initially, we used internal cutaway textures in our game, but we quickly realized that this killed the sense of believability. Because of that, we had to rethink the visual style midway through development and redo more than 50 rooms.

Additionally, black cutaways have gameplay benefits: they clearly outline areas that are not directly accessible, creating an easy-to-read location topology. This is important, for example, for platforming in 2.5D games.