If time is a constraint and it's not about racking up miles or bragging about crossing the country as fast as possible why wouldn't they just "fly/drive" to somewhere really special and do day rides out of a base camp for the time they have? Saying you rode across North America is pretty cool, saying you did it in the shortest time possible seems like a waste regardless of doing it for 50, 80, or 100 miles or 3000. Like I said I don't understand.
Not sure where you came up with a 25-mile a day limit but ok. Are you asking if an expensive ebike is worth owning? I'm surely not going to try and walk 25 miles a day with the comforts I want on my back. The times I do only shift base-camp 25+/- miles I still usually ride 50 or more miles each day I am there. I found a fishing hole once about an hour after having packed up camp, maybe 12 or 15 miles away that was so hot I had to spend a day. I had ridden the area some on preceding days but it was too good to pass up. The "overhead" you are referring to I think is quality, durability, having more power or capability than you need rather than less. The ebike and gear I carry on it allow me to travel in the style I like and stay in places that people in cars can't get to easily or at all.