Few core developers (mainly, one, Armin) that couldn't be bothered enough. It's a volunteer project after all.
He did write about the unicode problems with the Python 3 changes and the need for an improved WSGI spec (heck, he even co-wrote the unicode literal change PEP).
But after the new WSGI spec was out, and the u thing was already implemented in 3.3 pre-release, there was no much motion in Flask, whereas Pyramid, Django and others have already started work.
Even the "When will Flask support Python 3" document has not updated and is 2 years out of date in it's contents.
He did write about the unicode problems with the Python 3 changes and the need for an improved WSGI spec (heck, he even co-wrote the unicode literal change PEP).
But after the new WSGI spec was out, and the u thing was already implemented in 3.3 pre-release, there was no much motion in Flask, whereas Pyramid, Django and others have already started work.
Even the "When will Flask support Python 3" document has not updated and is 2 years out of date in it's contents.