Hello Procter,

To my knowledge, some airlines just don't make long(er) layovers easily bookable because it increases their liability/responsibility if you don't make it to your next flight. Therefore, many of the itineraries visible on Google Flights or otherwise the ITA Matrix, are not visible to the common customer, but are indeed bookable by travel agents or otherwise people with enough experience to go around the system.

Next time, you could try to consult a travel agent, try to see if OTAs have the option, or otherwise, try to book your flight with the Multi-City option.

Cheers