Drupal is not "so messy" IMO. It is so clean. Have you looked at other similar projects? I suppose this is a matter of taste.
I also don't think it is messy, at least not more then other similar projects :)
Coders who want to contribute to core don't just just focus on "speed, efficiency, and nice code" if they want to get their patch accepted. You have to get everything exactly right. You have to use a form group around multiple related controls, you have to use css in a sparse manner, you have to use a sortable table when data might want to be sorted. And so on. Skip any of those steps (and many more) and the patch languishes.
I also experienced this while my submitted messy locale interface plan was up for review, there was a lot of criticism on the UI, and finally a quite useable result ended up in Drupal. True, the guidelines we followed while fixing useability problems in that interface were not set on paper, and were probably not as clean as those that are going to be shaped. So I would only opt for saying that Drupal is good and is going to be better, not that it is messy and it needs to be good at least :) Goba