A responsibility does not have to be software
Line four of the manifesto is the one most architecture writing skips. Responsibilities may be fulfilled by people, partners, manual processes, or software capabilities.
This is not a concession. It is a design choice. When you model a responsibility before deciding how to fulfil it, you have options. A concierge capability at a hotel can be a trained human, a third-party service, or software — or all three, with a common interface. The responsibility is the same. The fulfilment differs.
Capabilities are the software realization of responsibilities. But not every responsibility needs to be a capability yet. Some responsibilities should stay with people. Some should be outsourced. As the organisation's capability matures, the same responsibility can shift from a person to a partner to software — without the model changing. The architecture accommodates all of them because it models the responsibility, not the implementation.
This is what makes a business architecture extensible over time. New ways of fulfilling old responsibilities can be introduced without redesigning the system.