Centralized in this instance means one provider controlling the platform. GitHub is owned and controlled by Microsoft and therefore has a descent amount of vend

Centralized in this instance means one provider controlling the platform. GitHub is owned and controlled by Microsoft and therefore has a descent amount of vendor lock-in. Email is not controlled by a single provider and if configured correctly, you can easily migrate email between various providers or host it yourself. Email uses open standards. A mailing list is centralized, but much less so than GitHub and is secondary in this instance.