Make external (guest) users be able to use "Only people in your organization" links

I just came across this post after verifying with support that sharing with 'people with existing access' does not include guests of the tenant, even if they already have access to the site. This makes no sense to me as it forces me as an admin to have to either route all external sharing duties (even sharing with people who already have access) through a site owner, or allow internal users to share the site without the owner's knowledge.
Hopefully Microsoft will change this at some point.