John Goering - Intune App Protection policies ensure the data cannot be leaked to unprotected apps. Syncing the corporate calendar data from Outlook into the native app would bypass the APP and allow the data to be shared to unprotected apps/services. Calendar events can contain fairly sensitive information just in the subject alone (e.g., HR, merger/acquisitions/divestitures, etc.). The same is true for contact sync, which is why we introduced via App Configuration Policies, a way for customers to limit the contact fields that are exported. Some customers lock it down such that only first, last and phone number are exported, others restrict certain fields like the note.
In any event, we have chosen to do native calendar import into Outlook as the first step because the Android ecosystem enables users to have a gmail account for personal usage and it is likely the user may be using the native apps. Calendar export requires additional thought and implementation to ensure data leakage doesn't occur.