Helpful, our local Moetza Datit put out a sheet about various dinim for the 9 days, erev Tisha b’Av. Tisha B’av, and the day after. It mentions that minhag Yerushalayim is to wear tallit and tfillin during shacharit on Tisha b’Av. I do remember seeing this when I was at the Kotel a few years ago on Tisha b’Av morning.
If I remember (and there are any left in shule) I will bring it home tomorrow and list the source quoted.
Perhaps the reason is, tzitzis are our “contract” with Hashem, illustrating our commitment to observe mitzvos and not to go astray. Since Tisha B’av is not the day to be touting such a broken promise, we try to keep a low(er) key until late afternoon when talis / tefillin are back on the agenda (just a thought)