The thing is, bikes like the 720 were good at the time and some of the best that were available. With the standard diameter tubing they were using before the era of oversized tubes they were not optimal for the job at hand. Gearing at the time was 3 x 6 with a good range but was still meant for a young person in their prime to move it along the road. We are better served today by the touring bikes we have to choose from and with the selection of components available than what we had to choose from back then.
Fortunately some builders came along and applied some thought that was needed to build some proper bicycles and not just build them because the lugs they could purchase would fit a 1" top tube. They have come up with some much better bicycles than existed back in the day. A Surly LHT purchased today, while probably not as esthetically pleasing in some ways as a Trek 720 was when new is a much better bicycle for doing the job at hand than a 720 is, not that many a person was prevented from doing some pretty good trips on the 720 they owned.