All of these are often of little concern to artists, who prefer to get in the flow of actually getting stuff done. Organizing your project is fun and all, but there's A TON value in eliminating context switches and shortening your iteration loop. Source: I participate in game jams.

Obviously, it would be nice to follow this up with refactoring, but you could also spend this time on another project, of which the author has many (and likely thanks to this "fire and forget" attitude).

I'm sorry, but it's not obvious to me how splitting the code into more files gives you any of these things except less mixing of HTML and JavaScript (which doesn't seem like a problem unless you have tools that won't handle it). Aren't these aspects of the code itself?