Windows Defender Application Guard Standalone mode

I think perhaps you misunderstand the intent of the feature.  I see primarily it as a sandboxed browser session that effectively runs each page in a VM, therefore eliminating any possibility of attacks affecting the core OS.  The features about favorites, history etc. they talk about and say they are being implemented in a later release.  As for enabling by default, I am sure this will be a Group Policy preference that organisations can set as they need.  Some business has VERY critical data that cannot be compromised in any way, so this is a worthwhile feature and it has been, in my experience, the very high-end employees that are most likely to be fooled by website attacks, spoofing etc. so intelligence, age and wisdom are irrelevant with modern IT attacks :-)  I do agree it will be a useful addon to the novice home user, or Grandma, but let's help MS get the feature tested and stable, then perhaps the rest will come.

Application Guard feature just like Credential Guard and Device Guard depends on underlying feature called Virtual Secure Mode. Which depends on Hyper-V and is Controlled by Group Policy and all these features are available on Enterprise Edition only. Virtualization extensions might or might not be present on all underlying hardware, though mostly they are present now a days.

Hence the reason for this to be available on Enterprise edition only.

Refer:

application-guard-microsoft-edge

credential-device-guard