There are a couple of relevant things going on here. The building you have pointed out as “nice” texture is actually modeled in 3D, including the relief and the architecture and the windows. Many of the buildings, including the one you labeled “ugly”, are actually flat sided boxes that have been painted with a texture photo on the outside. This accounts for some of the difference in the qualities you are seeing. If you set the style monochrome you can see the raw geometry under the textures to make this clearer.
This can be an acceptable way to represent buildings depending on how it’s going to be used. However, some of the base images used to paint the buildings are better than others, which is most likely just a product of what was available. The one you pointed out as ugly is particularly low resolution. Select the face you want see the image for ( just the face, not the edges) right click and choose Texture>Edit texture image, to open image in an outside image editing software You can also access this feature from the material picker in the colors in model list. As you can see that one is very low quality, you will need higher resolution better pictures of every side of the building to improve on this. This is really not bad considering the quality of the image, it’s well mapped and covers all sides which can be hard to do without getting professional photos taken from every angle.
There are some reversed faces and quite a bit of raw geometry (not in groups or components) , and not great use of tags here so be careful poking around the file as it would be easy to break. best to save a backup before trying to alter it.