I believe there are as many reasons for why people choose a bike to tour on as there are people. There are no right or wrong reasons, just differences.
At one of the spectrum are those who tour, and having a bike along is incidental to the travel. For some of use closer to the other end of the spectrum it "is about the bike". The sole objective is to tour on a bike, and the places are incidental.
I think the disposable bike might have merit in some situations, I think the disadvantages would outweigh the benefits, if the the ride was longer than a week or two. Also the cost of obtaining a disposable bike and outfitting it would cost just about as much as shipping my bike anywhere in the world. When I spend 2-3 months on my bike, I really want it to work for me. In my experience the cost of shipping our bikes has been a relatively small proportion of the cost of our trips in the 2-3 month range.
Even for us who tour on a regular basis, a trip ruined by an ill fitting bike or mechanical failures would be a disappointment. However, for those folks doing their "once in a lifetime" trip, it would be a disaster. I believe that the more important the trip, the more important the bike becomes.
The non-touristy spots, small remote villages, and remote places can all be experienced on a well fitting reliable bike.