Because you obviously need to add that feature to service b before anyone can use it. This goes for anything in software, libraries, products, APIs etc. Ideall

Because you obviously need to add that feature to service b before anyone can use it. This goes for anything in software, libraries, products, APIs etc. Ideally that feature should be developed indepedently by the team looking after that service. It could however be a feature request by another team. Once the feature is ready, you deploy it and then advertise this feature is now available. If it's a breaking change, you version it so it doesn't effect existing services. Then the team for service a can now start integrating that feature into their service. You don't need complicated orchestrated deployments. The time from service/team b advertising that the feature is available, to service a acutally consuming it may be weeks. You just treat the microservices as separate products exposing a API, which operate on different timelines. Other teams may request features, but the team maintaining the service determine the how and the timeline. Obviously higher priority items get developed first.