Many SDWAN architectures are based on a hub and spoke configuration. Although spoke to spoke communications are also possible via a matrix topology, the fundamental driving force on this not being important is that the most significant traffic flow is always between a branch office and the data centre and not between branches. A cited reason for branch to branch communications is alternative paths or resilience. Practically, faults at the branch office are lollipops. The last mile connection itself fails and there is no east or west bound path alternative on the failed last mile. As an example, if fibre fails then wireless backup would be the only alternative and not an alternative fibre path. However, in a data centre location these types of alternative fibre paths are available but it is disingenuous to assume that a data centre and branch office would have the same level of connection ability or requirement.
Read the article over at LinkedIn here.