Because it's a major part of the look-and-feel of the site and we don't change that without a good reason. Actually, we pretty much don't change that ever.
I would say the classic mistake is arbitrary redesign. Users hate change. Not inflicting random change on them is one of our secret weapons. Not saying we'd never do it, but there's a hierarchy of problem importance, and "need to have meaningful YC launch titles" is multiple levels below "don't inflict arbitrary change on users".
