Because technology shouldn't surpass real human interaction.
Wanna world from Matrix movie?
And as with anything else in life, we must weigh the options. Face to face can indeed be better than remote. It can also be worse, because some people just irritate others by their presence and little behaviors. But more significantly, some of us do work which requires a good amount of thought - uninterrupted, quiet thought. Shared offices make this more difficult (compared to a quiet home office).