Software archivists want a specific version of Office 365 from a specific month. Since Office 365 updates constantly, the "version" you download today might break a legacy macro you wrote three years ago. A verified ISO represents a frozen point in time.
Personal subscriptions usually download a small Setup.exe file (approx 5MB) which then streams the rest of the data from the cloud. A full offline ISO is generally reserved for Enterprise/Education to save bandwidth on mass deployments. ms office 365 iso verified