For about price of land and connectivity - in large city land price begin on few millions dollars per square kilometer, and usage of cable channels could cost from 50$ per meter (easy could be 200$/m).

Plus, space arrange could last years.

Heat dissipation in range of megawatts could be just prohibited by local regulations.

So, space in large cities is very serious problem, and for business it is usually easier to "compress" as much computing power as possible in one rack.