If the entire Constitution is about concrete matters comparable to 'building good-looking cities', and 'building good-looking cities' is certainly one such matter because it is emphasized in the concluding remark, then why would the word appear only once?

I don't believe abruptly inserting a term that's never mentioned is good writing style.

A plausible way to understand it is that, the concluding remark is a summarizing call-to-action, laying out the spiritual and ideological framework for the rest to act upon. It certainly needs to be abstract, just as the four words preceding 美丽.