Most bike tourists that I have noticed have the tops of the handlebars about the same as the top of the saddle if they use drop bars.
That is quite a few inches higher than racing setups. But if their reach is different than "average" if there is such a thing as average, they may have the bars higher or lower. For example, my folding bike has much shorter reach than my touring bikes and to compensate for that I have the bars a couple inches lower so that I lean forward about the same as I do on other bikes.
When I use the drops instead of the hoods or handlebar tops, I usually can pedal in a gear that is about 10 percent higher at the same cadence if I have a strong headwind. No or weak headwind, does not matter if I lean forward or not.
If I was sitting more upright, I would have less weight on my hands, more on my bum, and my saddle would get uncomfortable sooner.
I think that you will find most bicyclists on touring bikes have set it up so that it fits best for them for long days in the saddle. Sometimes it is best to just use what works best instead of trying to re-invent the wheel. I have a lower back injury, my saddle is turned slightly to the left because that fits me better than straight ahead. We all set up our bikes so it works best. And for touring, what works best is that you feel better day after day of long days in the saddle than if you had a different setup. What works best for a racer has nothing to do with comfort, for them a wind tunnel or stopwatch is used to measure what is best.
And things change, as people age they often will want the bars a bit higher. A bit over a decade ago I lost about 15 percent of my body weight, that shrunk my pants waist size by quite a bit, and after that I found that my bars felt better if I lowered them a bit. I also found that, using the drops was much more comfortable after the weight loss. But I have seen people with a huge beer belly that want to sit straight up if they can, leaning forward for them is not comfortable at all.
In other words, your final question, "Why are tourists doing it?", they are doing what works best for them.
Side note: That guy on the Surly in post 1 is going down a hill, thus any angles you get are not applicable to riding on flat ground. The LHT has a top tube that slopes slightly towards the rear, but the bike in the photo has a top tube sloping slightly the other way. His bike also looks like it has a longer than stock stem, I am guessing that he bought a different stem to make the bike feel more comfortable. I can't see the saddle on that bike but I am guessing that his saddle is higher than his handlebars. A lot of people wanted to buy a shorter stem, not longer after buying a LHT.