In very broad terms, it's a competitiveness factor. The ability for travellers to arrive in the U.S. as domestic travellers and just step outside and get into their taxi within 15 or 20 minutes is a tremendous advantage relative to travellers from other countries. It's part of a broad package of what airports are doing with partners in the air carrier world to be more competitive against hubs in other parts of the world: providing a better passenger experience and reducing time required as well.
On May 29th, 2017. See this statement in context.