As an Microsoft 365 subscriber why can't I just install Office Pro Plus myself?

Doing so will violate the agreement with Microsoft. Under the terms of the program, Microsoft 365 must be installed in Shared Computer Activation (SCA) mode. This installation mode is different to a normal retail or volume license installation. Please use the Microsoft 365 License form to register your Microsoft 365 licenses for use with Zettagrid and we will provide the relevant Office deployment tool and configuration file.