I actually just finished writing a whole PhD thesis on that topic! You can skim it here: https://sourcecode.enframed.net
Some interesting parts were about the metaphors that people use to make sense of 'pretty' code (is code like prose? like poetry? like maths? like architecture? are any of those craft activities?), and about the role of tools (from IDEs to languages) in affecting what we consider to be nice or not.