Analog provisioning is typically more expensive and avoided. One year warranty is typical. Contracts must be negotiated for the PBX life. System upgrades and expansion require capital outlay when needed. It is very expensive to provide the same level of preparedness.
Organizations often wait for repairs when problems occur.
Expensive additional resources are required to manage the phone system. Deployment of features is at will. Management of system is immediate on an as needed basis. Most features are paid for initially, once. Major equipment costs are incurred up front, once.