Security, maybe some of us are accessing the community in public places (not using public wifi), so you don't want any prying eyes see who your are if you see that you are in the bitcointalk forum.
But is there actually a need for this extra security, even after knowing we are all anonymous in this forum?
Most times we use our phones when we are free and less busy, so why the need to remove the welcome name from the home page of the forum?
Some people may actually feel unsafe with that, but I am always happy to see my username displayed on the home page.