No airplane trip lasts three days. Can you imagine a cruise ship with cabins without private bathrooms? The whole concept of the long distance train needs rethinking. Australia and Canada have transcontinental trains that function as cruises on rails. Canada seems to do the best they can with very old equipment. Australia has better rolling stock. I think all accommodations on the Indian-Pacific have private bathrooms. Under the former Amtrak administration the goal seemed to be to get out of long distance service. That may not have changed. Unfortunately the only major directive Congress has given Amtrak is to cut costs. No-one seems to have any philosophy regarding the purpose of long distance trains which could be a national asset. even an international tourist attraction, if they were competently developed if allocated enough funding. With the current health crisis and the economic fallout, Amtrak will be a very low priority.I actually have stayed in a hotel (Pod 51 in NYC) as recently as this January that had shared bathrooms in the hall. Everything was clean, the room was small (even by Manhattan standards), but I paid less than $80 a night. I've stayed in any kind of accommodation that came with a private unenclosed toilet in the room. Other than Viewliners the only other modern accommodations set up like that are prison cells. I've stayed in other micro hotels that bathrooms, but the toilet & shower were still in an enclosed cubical.
Sleeping cars are an extremely tight squeeze and shared facilities make more sense when trying to fit as many revenue spaces in as you can and still give everyone a bed. And the Viewliner II's still have options for passengers who want en-suite facilities. Even on airlines with First Class "suites" passengers still share bathrooms.