Like, there's no one way to simplify a background. How do you simplify anything?
When you look at a tree you want to draw in the foreground, what do you do with clumps of thousands of leaves? When you want to draw a cat from a reference photo, what do you do with all the fur? The advice I've given to friends has always been to reference Shapes rather than Details, but how that manifests is going to depend on how you personally draw -- whether you use spot blacks or hatching or little scribbly line details or simple blocks of colour -- all of those are fine abstractions to use, depending on what you're comfiest with (which is more or less what a "style" is -- what abstractions are comfiest for you?).
Those ideas don't change when it's buildings. You still have to find the basic shapes of light and shadow and the basic shapes of the form, the same when you're drawing a tree, the same when you're drawing a dog, the same when you're drawing a human.
I do notice that all the artists you're pulling from aren't drawing "backgrounds" so much -- they're drawing environments. There are buildings in the foreground of those illustrations that then move further back and become less detailed. By contrast, you've chosen a reference photo that cannot really be an environment in that way -- it's just a backdrop. So, yeah, if you learn how to draw buildings in that sense -- as a backdrop to an unrelated scene that's happening in the foreground -- I think it would be natural to struggle with figuring out how to make that fit in with the same style you use to draw characters. Those two things literally don't fit together.
Photos like this are still skyscrapery, but it has a more human scale. You can put a character in this. You have to draw buildings that are closer, and then buildings that are farther back, and then buildings in the "background."
For me, this kind of reference helps me a lot more when I'm trying to understand environments; I personally find it difficult to take anything of use from the "backdrop" type photos. When I was learning to draw the style of architecture in tuscany for my comic, the huge city-wide panoramas of a thousand tops of buildings weren't as helpful until after I'd sketched some reference of buildings in a more human scale, so I could understand them more solidly and have a better feel for their shapes and important details.
If you're using a ruler for this, it might be good to put down the ruler for a bit and sketch. Sketch out scenes and environments from references without using any ruler at all. It's easier to steer yourself away from getting caught up on details when you're sketching out a basic form, just trying to get the right shape of it and make it look nice as a sketch -- it's a lot easier to start to get a feel for what details you need.
Those illustrations you're studying weren't the result of staring at a reference really hard until something clicked -- they're much more likely the result of so many studies of similar elements from references that the artist really had a feel for how to sketch out the components of a city by the time they drew these -- the designs feel simplistic and "right for the story" not because you're missing something obvious, but because those artists have taken the time to become comfortable.