Why does Microsoft not sync the Global Address List (GAL) to iOS and Android devices?

Because Microsoft has architecturally and strategically not planned it.
The missing mobile GAL synchronization is not a bug or a configuration issue, but a deliberate design decision that has not changed for many years.

Microsoft confirms this itself:

“It is not possible to sync the entire GAL to your mobile device.”

The reasons for this are fundamental:

1. Architecture

The Global Address List is a directory service, not a contact folder.
Mobile sync mechanisms like Exchange ActiveSync or Outlook Mobile synchronize mailbox content exclusively – the GAL is intentionally separated from this.

2. Platform limitations of iOS and Android

Apple and Android only display account-based contacts in the native address book (e.g., iCloud, local Exchange contacts, CardDAV). Directory objects like the GAL cannot be integrated system-wide there.
→ no native caller ID, no voice control, no access from the phone app.

3. Strategic decision

An automatic distribution of all company contacts to mobile devices raises questions about data protection, device ownership (BYOD vs. corporate device), and scalability. Microsoft has not addressed this use case for years and effectively refers to third-party providers.

This topic has existed unchanged in Exchange environments for decades.