* Most people are much more used to them. This doesn't make them better, but it does make them a feature people dislike living without.
This summarizes perfectly my opinion. I don't think it's a positive thing, though... I love Sublime's design and personality, and the new tree view looks like compromising both. However, if the majority of users ask for it, then there's little that can be done about it.
* Tree views are much better for things having to do with exploring the project. For example, on a new project, I like to look around it to see what files there are, what the directory structure is like, etc. This makes it much easier.
* Creating new dirs/files is also much easier when using a treeview.
Maybe I'm too used to use the command line, but these things seem to fall out of Sublime's scope at the moment. I consider it a text editor, not a file browser. In any case, I see your point.
* Potentially, specifying searches on subdirs could be much easier with a treeview.
The current search in project feature is quite solid. I think the tree view is convenient because it's familiar, so we're back to point #1. I'm not claiming that the existing features are perfect, but I'd much rather see them evolve than see the editor's become less consistent and--worse yet--more mainstream. On the positive side, this is probably a sign that it's doing well commercially.
Also, even tree views are becoming obsolete in OSes in favour of search, which is what Sublime offered up to now.
I'll try to be more constructive later by posting some ideas to add to the quick panel view and maybe even to the project panel.