Node sieges require a lot of coordination and are very difficult to actually succeed in. Especially if it is a metropolis, than a Siege will need to be a mass effort, and if one Node falls another one will rise faster unlocking more unique content to that other zone.
It can be obnoxious I am sure but that is why they want the node system to be so varied, a Divine metropolis may fall but a scientific node in another zone may rise.