Axiomatically, socially the sum of two humans is greater than the two humans apart.
And large cities, with metros, many villages that melt into one, employment opportunity, talks, bars, etc, are the embodiment of what it means to be social (with some exceptions - community feel being an important one).
In the UK this is at the forefront of politics - it is obvious to anyone that the country is governed as 'London plus appendages'. The rail and road networks are basically built around the capital. Most public transport subsidies go to the capital. The important (in a status sense, not in an absolute sense) businesses are headquartered there.