Experts who refuse to believe something can be simply because they assume it cannot be should not be referred to as experts.
It’s silly given the number of large private roman residences built in rural out of the way areas in say Switzerland. You realize there would be no reason for this unless cities and the travel routes were much more populated, utilized and connected than they previously imagined. The elite class built vacation homes on places like the island of Elba. Many sites have just not been found, as they are lying beneath farm fields, and until they need to place sewer pipes will likely not be found.